Virtual Oscillator Control for Synthesising Virtual Inertia in a Smart Transformer-Based AC Microgrids
Gaurav S., Kumar C., Liserre M.
Article, IEEE Transactions on Industrial Electronics, 2026, DOI Link
View abstract ⏷
The smart transformer (ST) is a power electronics-based transformer that serves as an energy router and provides various ancillary services in the electrical distribution grid. However, an ST-based microgrid has limited inertia, leading to frequency instability, sustained voltage oscillations, and synchronization problems during disturbances such as load changes, line switching, generation loss, etc. In this article, a new virtual inertia control is proposed for the ST low-voltage (LV) converter and distributed generation (DG) converters. The proposed adaptive decentralized virtual inertia-virtual oscillator (VI-VO) control for ST-based microgrids provides frequency containment reserve (FCR) services and offers fast dynamic response with time-domain implementation. It further enables accurate power sharing among converters, improves frequency characteristics, ensures stable operation under varying operating conditions, and eliminates the need for phase-locked loop (PLL). In addition, the proposed controller allows the ST LV converter to support frequency restoration reserve (FRR) service in the microgrid. The eigenvalue analysis demonstrates the small-signal stability of the proposed system. The simulation and experimental results are shown to verify the performance of the proposed virtual inertia synthesis.
Inductor Current Ripple Suppression in Dual Active Bridge Converters Using Finite Control Set Model Predictive Control
Meikap S., Kumar C., De Morais Carnielutti F., Rodriguez J.
Article, IEEE Transactions on Industrial Electronics, 2026, DOI Link
View abstract ⏷
Dual active bridge (DAB) converters are extensively used in isolated bidirectional DC–DC power conversion systems for EV charging applications. In DAB converters, inductor current ripple remains a major challenge, leading to conduction losses, thermal stress, and reduced reliability specially during light loaded constant voltage (CV) charging of battery. In this article, a finite control set model predictive control (FCS-MPC) is proposed for inductor current ripple suppression. In comparison with the existing methods where rms inductor current is reduced without considering ripple reduction, the proposed FCS-MPC develops a new discrete-time inductor current prediction model using the leakage inductance and parasitic effects for accurate inductor current estimation. Moreover, the weighting factor of the proposed FCS-MPC is optimized for ripple current reduction using Newton–Raphson optimization method. A SiC–Si asymmetric bridge configuration is employed to ensure real-time execution, with the high-frequency SiC stage executing the predictive control and the low-frequency Si stage reducing switching losses. Compared with proportional–integral (PI)-based single-phase-shift control, the proposed strategy reduces inductor current ripple by 10%–15% and total harmonics distortion (THD) by 2%–8% under light-load operation. Simulation and experimental results are shown to validate the inductor current ripple suppression capability of the proposed method.
Numerical Investigation of Steady Natural Convection from a Heated Cylinder Enclosed in Inclined Square Enclosure
Kumar D., Kumar C., Gupta A.K., Baranwal A.K.
Book chapter, Springer Proceedings in Materials, 2025, DOI Link
View abstract ⏷
This study explains the result of natural steady convection that originates from a heated cylinder within an inclined enclosure. The convection processes occurring due to the temperature differences among the heated cylinder, heated walls, and the cold walls of the enclosure were investigated using different dimensionless numbers (Grashof and Prandtl numbers). The Grashof and Prandtl numbers span from 10 to 104 and 0.7 to 90 respectively. A numerical solution to the governing partial differential equations was obtained. The intricate flow patterns visibly represented by the streamlined contours when Prandtl and Grashof numbers were applied. Convection currents could be found around the heated inner cylinder, demonstrating how buoyancy-driven forces played a pivotal role in shaping the circulation in the annular space. Isotherm contours illustrate thermal gradients and the impact of buoyancy-induced flow. The local Nusselt number distribution can be used to determine the various contributions made by dimensionless numbers to the heat transfer rate. Data are often displayed using variations in the average Nusselt values on the cylinder surface. The local Nusselt number was used to find out how much convective heat transfer occurred at a specific location on a surface compared to conductive heat transfer. Heat transfer outcomes can now be predicted in a new application because they have been observed as a function of Grashof and Prandtl numbers.
Reverse Startup Procedure for Multi Terminal Smart Transformer Supplying Data Centres
Anandh N., Das D., Kumar C.
Conference paper, 2025 IEEE Guwahati Subsection Conference, GCON 2025, 2025, DOI Link
View abstract ⏷
A reverse startup procedure for a multi terminal smart transformer (MTST) supplying data centres, transitioning from islanded operation to grid connected operation is proposed in this paper. During islanded operation, the MTST low voltage (LV) converter remains active, while the MTST multi active bridge (MAB) converter is partially active and MTST medium voltage (MV) converter is inactive. To facilitate reconnection to the MV grid from the LV side, these converters need to be activated to allow the power flow. In this operation, the power is drawn from a battery energy storage system (BESS) connected to LVdc-1 bus to charge the MTST MVdc bus. Once the MVdc bus is sufficiently charged, the MTST-MV converter is initiated to establish the connection between the LV side and the MV grid. Simulation is performed in PSCAD and the results are provided to validate the effectiveness of this startup operation.
A Wavelet Transform Approach for Short-Circuit Fault Diagnosis in Smart Transformer-Based Meshed Hybrid Microgrids
Rao L.K., Gaurav S., Kumar C.
Conference paper, National Power Electronics Conference, NPEC 2025, 2025, DOI Link
View abstract ⏷
This paper presents a fault detection and classification strategy based on the wavelet transform (WT), utilizing current signals in smart transformer (ST)-based hybrid microgrids. The Haar wavelet is chosen as the mother wavelet function to extract features from current signals due to its effectiveness in capturing critical fault characteristics. Fault detection is performed by identifying the maximum values of the detail coefficients of the AC currents, while fault classification is achieved with the help of the maximum detail coefficients of the three-phase AC currents along with the ground current. The proposed method demonstrates reliable performance under various fault scenarios, including different fault types, fault location, fault resistances, and ground resistances. This approach is effective in detecting both symmetrical and unsymmetrical faults, ensuring accurate classification across diverse fault scenarios. The proposed method is validated on an ST-based LV meshed microgrid model developed in the MATLAB/Simulink environment.
Virtual Oscillator Control-Enabled Unbalanced Fault Ride-Through in Smart Transformer-Based AC Microgrids
Gaurav S., Rao L.K., Kumar C.
Conference paper, IEEE PESGRE 2025 - 4th IEEE International Conference on Power Electronics, Smart Grid, and Renewable Energy, 2025, DOI Link
View abstract ⏷
Smart transformer (ST)-based microgrids are preferred over conventional power transformer (CPT)-based microgrids because of their compact size, lighter weight, and ability to provide ancillary services. The low-voltage (LV) converter of ST operates as a grid-forming converter (GFC) unit, and distributed generator (DG) converters follow the voltages set by the ST LV converter. This paper introduces a new control technique called the instantaneous symmetrical component-based Andronov-Hopf virtual oscillator (S-AHVO), which addresses the limitations of existing virtual oscillator (VO) controls that only synchronize with positive-sequence voltages and fail under unbalanced conditions. The S-AHVO control enables continuous synchronization of positive, negative, and zero-sequence voltages, thereby enhancing microgrid operation during voltage imbalances and ensuring accurate load sharing. It maintains the dynamic performance of existing VO controls and can be implemented without additional sensors. The paper includes a systematic design procedure, mathematical analysis, and simulation studies to validate the proposed technique.
Grid stability and power quality improvement in electric distribution systems using smart transformer
Manojkumar R., Kumar C., Ganguly S.
Book chapter, Design and Control of Active Power Filters towards the Decarbonisation of Smart Grid Networks, 2025, DOI Link
View abstract ⏷
The ancillary services are important for maintaining the grid stability and power quality in modern power systems. High penetration of renewable energy sources and increase in the loading levels lead to voltage rise and voltage drop in the distribution network, respectively. Therefore voltage control is an important ancillary service in distribution systems. In this chapter the use of smart transformer for voltage control in low-voltage (LV) distribution systems is discussed. There are two types of voltage-control methods, that is, set points–based voltage-control method and full output voltage range–based method. In set points–based control the output voltage is chosen from the predefined set points. In a full output voltage range–based control, the output voltage is infinitely adjustable within its range. The application of both these voltage-control methods for improving the voltage profile in LV distribution network is presented through different case studies.
Performance Analysis of Modular Multilevel DC-DC Converter: Impact of Arm Inductors
Pallath A., Malviya H., Kumar C.
Conference paper, National Power Electronics Conference, NPEC 2025, 2025, DOI Link
View abstract ⏷
Recent advancements in transportation electrification have led to more demand of efficient and fast electric vehicles (EVs) charging infrastructure. To support fast charging of electric vehicles, modern EV charging stations utilize high-power DC-DC converters operating on high DC voltages. This paper presents the design of a Modular Multilevel DCDC Converter (M2DC) and compares two configurations: one incorporating dedicated arm inductor (M2DCL) and the other without arm inductor (M2DCNL ) to analyze their role in system behavior. The topologies are tested under identical operating conditions to evaluate and compare key parameters such as arm current, submodule (SM) capacitor voltage, load voltage, and load current. Both systems are tested in voltage control mode of operation. The comparitive analysis has been done on the basis of experimental results obtained from the scaled down prototype of M2DC.
Double Pancake Spiral Coil based Wireless Power Transfer System for EV Charging
Vishwakarma A., Gaurav S., Kumar C.
Conference paper, 2025 IEEE Energy Conversion Congress and Exposition Asia: Shaping a Greener Future with Power Electronics, ECCE-Asia 2025, 2025, DOI Link
View abstract ⏷
Several designs of non-polarized coupling coils for wireless power transfer (WPT) systems are available, such as flat circular and rectangular coils. However, they typically have limited power transfer capacities and are restricted to shorter distances. This paper presents the design and development of a double pancake spiral coil-based WPT system. The polarized coil is made using two flat pancake-type coils connected in series with additive polarity to enhance the magnetic field density. The steps for designing the coil structure are discussed in detail. The FEM analysis for measuring the self and mutual inductances of coil structure at different distances is done in Ansys Maxwell 14.0 software. These inductance values are also verified through the developed experimental setup. The setup operates at different distances and switching frequencies to observe variations in the efficiency of power transfer.
Chopper Circuit based DC Voltage Balancing in Neutral Point Clamped Dual Active Bridge Converter
Rishitha P.M., Meikap S., Kumar C.
Conference paper, 2025 IEEE Energy Conversion Congress and Exposition Asia: Shaping a Greener Future with Power Electronics, ECCE-Asia 2025, 2025, DOI Link
View abstract ⏷
One of the major challenges in Neutral Point Clamped (NPC) Dual Active Bridge (DAB) converters is maintaining capacitor voltage balance. Ineffective voltage balancing can lead to several issues such as increased harmonic distortion, which degrades power quality and impacts overall system performance. It may also result in over-voltage conditions, potentially damaging components and reducing system reliability. Moreover, voltage imbalances contribute to higher energy losses, reducing overall efficiency and increasing operational costs. Beyond these issues, capacitor voltage imbalances can also cause thermal stress on converter components, accelerating aging that potentially leads to system failure. Additionally, they complicate control strategies, making it more difficult to achieve stable operation under varying conditions. To overcome these challenges, the integration of a chopper with carrier wave control is proposed, which aims to maintain voltage balance even in the presence of faults and switching irregularities.
Model Predictive Control based Adaptive Phase Shift Modulation for Neutral Point Clamped Dual Active Bridge Converter System
Meikap S., Kumar C., Rodriguez J.
Conference paper, 2025 IEEE Energy Conversion Congress and Exposition Asia: Shaping a Greener Future with Power Electronics, ECCE-Asia 2025, 2025, DOI Link
View abstract ⏷
In this paper, an adaptive phase shift modulation is proposed for a neutral-point-clamped dual active bridge (NPCDAB) converter-based battery charger. This is implemented using a moving discretized control set model predictive control (MDCS-MPC). The proposed control can adjust step size to reach reference point faster and also helps in achieving constant switching frequency operation, which are not possible with finite control set MPC with fixed step size. Also, the circuit analysis becomes simpler with fixed switching frequency operation. The performance of circuit is verified in MATLAB software.
Virtual Oscillator based Dual Loop Control for Grid Forming Modular Multilevel Converter
Malviya H., Gaurav S., Kumar C.
Conference paper, IEEE PESGRE 2025 - 4th IEEE International Conference on Power Electronics, Smart Grid, and Renewable Energy, 2025, DOI Link
View abstract ⏷
Modular multilevel converter (MMC) is widely explored for offshore wind farms and large-scale photovoltaic (PV) plants for high voltage (HV) and medium voltage (MV) power processing. The MMC comprises of sub-modules (SM) connected in series and can provide higher voltage levels. The dc-ac power conversion through MMC is done through grid forming (GFM) control to regulate voltage magnitude and frequency. In the GFM mode of operation, power converters are susceptible to low-order voltage and frequency oscillations and instability. This paper presents an Andronov-Hopf oscillator (AHO) based virtual oscillator (VO) control for MMC with dual voltage and current control to address such issues. The modulation scheme includes rule-based SM voltage balancing to maintain SM capacitor voltages. The simulation results show the stable operation of the MMC through load variations.
Asymmetrical PV Power Injection in Modular Multilevel Converter with Battery Energy Storage Systems for Ripple Power Reduction
Malviya H., Rodriguez J., Kumar C.
Conference paper, 2025 IEEE Energy Conversion Congress and Exposition Asia: Shaping a Greener Future with Power Electronics, ECCE-Asia 2025, 2025, DOI Link
View abstract ⏷
Modular multilevel converter (MMC) is widely explored for high voltage direct current (HVdc transmission) and medium voltage direct current (MVdc) applications. The MMC is made up of submodules (SM) that are connected in series. In literature, renewable energy sources (RES) is integrated to SMs of MMC. However, integration of RES with some of the SMs result in asymmetrical power flow in arms and SM capacitor voltage ripple. This also results in increased total harmonic distortion (THD) in ac current, more arm currents, and large circulating current. For mitigating such issues, this paper proposes a battery energy storage system (BESS) integrated at the SMs of MMC. A proportional controller is developed to control the power flow in proposed system to achieve the reduction in the dc voltage ripple of SM capacitors. This further helps in total harmonic distortion (THD) reduction in grid current. Performance of the system is verified using MATLAB/Simulink platform.
A New Method to Establish Smart Transformer-Based Meshed Hybrid Ac and Dc Distribution Grids
Kumar C., Gaurav S., Meikap S., Malviya H.
Conference paper, National Power Electronics Conference, NPEC 2025, 2025, DOI Link
View abstract ⏷
Smart transformer (ST)-based meshed hybrid microgrids consisting of ac and dc distribution lines have recently been proposed. However, such solutions demand laying of additional distribution lines in the electric grid for forming dc grids, resulting in additional costs and space requirements. Generally, the loads are predominantly single-phase with limited three-phase loads in the low voltage (LV) ac distribution grid. Considering such load composition in LV distribution grid, this paper proposes a new method to establish ST-based meshed hybrid grid consisting of ac and dc grids. The three-phase dcac power converter of the conventional ST is replaced with a single-phase dc-ac converter, and one of the phases of existing three-phase ac distribution along with the neutral wire is used for forming single-phase ac distribution grid. The remaining two phases of the existing three-phase ac distribution grid are connected to the LVdc link of the ST to form dc distribution grid. Single-phase distributed generation (DG) converters injecting power from DG systems are utilized to form the ac-dc meshed hybrid microgrid. A three-phase converter is used to support three-phase load by taking power from the LVdc line. The simulation results have been shown to verify the performance of the proposed configuration.
Observer-Based Control Using Super-Twisting Technique for a PV-Wind-HESS-Based DC Microgrid Feeding Constant Power Loads
Thomas T., Mishra M.K., Kumar C., Liserre M.
Article, IEEE Journal of Emerging and Selected Topics in Power Electronics, 2025, DOI Link
View abstract ⏷
This article introduces a novel control strategy for a dc microgrid with integrated photovoltaic (PV) and wind energy sources, combined with a hybrid energy storage system (HESS) comprising a battery and a supercapacitor, feeding constant power loads (CPLs). The supercapacitor's high power density is essential for absorbing transient power components, thus extending the battery's lifespan. However, tightly controlled power electronic converters in this system, which behave as CPLs, potentially lead to instability. To address this, a control method based on super-twisting control (STC) and modified super-twisting observer (MSTO) is proposed for the HESS's bi-directional converters. This approach improves the stability margin, enhances dynamic performance, and tightly regulates the dc bus voltage. In addition, a super-twisting sliding mode controller (STSMC) is employed to track the current reference from the maximum power point tracking (MPPT) algorithm under varying wind speeds in a permanent magnet synchronous generator (PMSG)-based wind system. Theoretical analyses and both simulation and experimental evaluations validate the effectiveness of the proposed control strategy in the PV-wind-battery-supercapacitor-based dc microgrid.
Virtual Oscillator Control of Series-Connected PV Powered Converters for MV Grid Integration
Gaurav S., Malviya H., Meikap S., Kumar C.
Conference paper, 2025 IEEE Guwahati Subsection Conference, GCON 2025, 2025, DOI Link
View abstract ⏷
Cascaded converters are used to achieve higher ac voltages with low-voltage semiconductor devices. The focus is on localized power transfer between low-voltage solar photovoltaic (PV) systems dispersed across converter dc links, with the converter ac sides being series-connected to a three-phase medium-voltage ac grid. Currently, decentralized controllers that enable power transfer in these systems are limited. To address this need, a virtual oscillator (VO) controller based on an Andronov-hopf oscillator (AHO) is proposed, enabling decentralized power transfer and utilizing only locally measured current. The approach allows for communication-free synchronization of the converter modules and does not require phase-locked loops. Since the VO control uses a time-domain implementation, it achieves superior transient response. The simulation results show the controller's fast response, grid synchronization, and effective power dispatch based on the PV power variations.
MPC-Enabled DAB Converter Control to Reduce LVdc Ripple in SST-Based Microgrid
Meikap S., Malviya H., Gaurav S., Kumar C.
Conference paper, IEEE PESGRE 2025 - 4th IEEE International Conference on Power Electronics, Smart Grid, and Renewable Energy, 2025, DOI Link
View abstract ⏷
Solid-state transformers (SSTs) are increasingly adopted for microgrids due to their bidirectional power flow capability, availability of medium-voltage dc and low-voltage dc (LVdc) links, and ancillary services. However, linear and nonlinear loads at the low-voltage ac (LVac) side introduce ripple into the LVdc link. These ripples cause capacitor stress, efficiency degradation, and deterioration of power quality. The conventional ripple mitigation techniques, such as oversized dc-link capacitors, passive/active filters, etc. increase the cost and volume of system, and limits the dynamic performance. Another conventional approaches include direct compensation that impose large current stress on the dc-dc converter. To address these challenges, this paper proposes a model predictive control (MPC) strategy for the dual active bridge (DAB) converter to actively suppress LVdc ripple in SST-based microgrids. The proposed method leverages a moving discretized control set MPC (MDCS-MPC) framework that explicitly models both second-harmonic and higher-order ripple dynamics, adaptively adjusting the DAB phase-shift angle for effective ripple mitigation. Simulation results demonstrate reduced LVdc voltage ripple, and improved voltage regulation under nonlinear load conditions.
Power Control in Andronov-Hopf Virtual Oscillator Converters for ST-Based LV Distribution Systems
Gaurav S., Pugliese S., Langwasser M., Kumar C., Liserre M.
Article, IEEE Transactions on Industrial Electronics, 2025, DOI Link
View abstract ⏷
Today’s distribution grid faces challenges in maintaining power flow and power quality due to the increasing integration of distributed generation (DG) units. The smart transformer (ST) is an effective solution to overcome these challenges by employing accurate control of both active and reactive power flows. Generally, the low-voltage (LV) converter of ST is controlled using a voltage-oriented control strategy, often facing issues with integral saturation and difficult parameter adjustment. Meanwhile, the DG converters operate in the current control mode, which leads to reduced system stability and poor synchronization, particularly during transient events and weak grid scenarios. To overcome these issues, this article proposes a novel Andronov–Hopf oscillator (AHO) circuit-based virtual oscillator (VO) control for the ST LV converter and DG converters in the ST-based converter-dominated LV distribution systems. This approach allows for simultaneous active and reactive power control of AHO-controlled LV DG converters, with the ST LV converter operating as a slack unit. Additionally, two integral control laws are incorporated to counter the remaining steady-state power errors caused by system uncertainties. The proposed control strategy is simulated in MATLAB/Simulink software and experimentally validated through a power-hardware-in-loop (PHIL) test bench.
A Meshed Hybrid Microgrid Configuration With Unified Power Quality Conditioner
Kumar D., Hrishikesan V.M., Deka A.K., Das D., Kumar C., Mishra M.K.
Article, IEEE Journal of Emerging and Selected Topics in Power Electronics, 2025, DOI Link
View abstract ⏷
The distribution grid is under major transformation due to the increasing dependency on renewable energy resources (RESs) and electric vehicle (EV) charging stations. For accommodating such sources and loads in an existing ac distribution system without violating the voltage and current quality limits, various strategies, such as modifying the control methodologies and structural reconfiguration of the grids, are identified as suitable options. The power electronic converters play a significant role in integrating these features to the distribution grid. A unified power quality conditioner (UPQC) is a preferred choice to control the quality of both currents and voltages. In this article, the operation of a meshed hybrid microgrid is realized using UPQC. The dc link of UPQC is used to form a low voltage dc (LVdc) line. This LVdc line is connected parallel to the low voltage ac (LVac) lines. The loads and distribution generation units are integrated to ac and dc lines using power electronic converters. The improved performance during adverse operating conditions shows the superior reliability of the proposed system. In addition, the analysis verifies the enhanced capability of the proposed system in accommodating new dc loads to the existing system. Both simulation and experimental results are demonstrated to evaluate the performance of the proposed system.
Applications and Services of Solid-State Transformers in Active Distribution Networks – A Critical Review
Wald F., Hrishikesan V.M., Gomis-Bellmunt O., Ji H., Davoudi M., Bidram A., Syed M., Josevski M., Bruske S., Kumar C., Alzola R.P., Colak I., Pannala S., Liserre M., De Carne G.
Article, IEEE Transactions on Smart Grid, 2025, DOI Link
View abstract ⏷
Distribution systems have traditionally received the least attention in the bulk picture of power systems; they are yet the most 'critical component' as they directly impact customers' perception and utilities' reputation. While transmission systems have seen abundant literature, innovations, and applications of power electronic-based devices to optimize their performance, distribution systems still require more attention toward a flexible and dynamic scheme to cope with volatile energy consumption and production. As a replacement or enhancement of the traditional ones, Solid-State Transformers can play a central role in the energy management of distribution systems towards this goal, in addition to the mere voltage conversion. This manuscript, developed within the IEEE Task Force on Solid-State Transformer integration in distribution grids, offers a critical review of the Solid-State Transformer potential, services, and technical challenges for its integration in distribution systems. Particular attention is given to scientific trends and open points in the current research that must be addressed before utilities extensively integrate the Solid-State Transformer in distribution systems.
Applications and formulation of bio-ink in the development of tissue scaffold: A review
Book chapter, Bioimplants Manufacturing: Fundamentals and Advances, 2024, DOI Link
View abstract ⏷
Three-dimensional (3D) bioprinting technology enables the fabrication of porous structures with complicated and variable geometries, allowing for the equitable distribution of cells and the regulated release of signalling components, which distinguishes it from traditional tissue scaffolding approaches. In 3D bioprinting, various cell-laden materials, including organic and synthetic polymers, have been used to create scaffolding systems and extracellular matrix (ECM) for tissue engineering (TE). However, significant technological hurdles remain, including bio-ink composition, printability, customizing mechanical and biological characteristics in hydrogel implants, and cell behaviour guiding in biomaterials. This chapter investigates several methodologies for hydrogel-based bio-inks that can mimic the ECM environment of real bone tissue. The study also looks at the process factors of bio-ink formulations and printing, as well as the structural requirements and production methods of long-lasting hydrogel scaffolds. Finally, contemporary bioprinting techniques are discussed, and the chapter concludes with an overview of the existing obstacles and probable future prospects for smart hydrogel-based bio-inks/scaffolds in tissue regeneration.
Three-stage receding horizon-based voltage control and electric vehicle charge scheduling of active distribution networks
Dutta A., Ganguly S., Kumar C.
Article, IET Renewable Power Generation, 2024, DOI Link
View abstract ⏷
In this article, a three-stage, two-level voltage regulation scheme based on receding horizon control (RHC) principles is proposed for active distribution networks. The distribution system consists of photovoltaic (PV) generators, electric vehicles (EVs), and electrical loads. Electric vehicle aggregators (EVA) act as intermediary between the prosumers and the network operators. The devised framework aims to coordinate various voltage control equipment according to their slow response (1st stage) or fast (2nd stage) response to voltage variations. In the 3rd stage, the electric vehicle charge scheduling is accomplished and all these stages constitute to form upper-level operation. Further, an effort has been made to maximize the profit of EVA for performing ancillary services during EV charge scheduling. Moreover, EVAs incorporate demand response programs to enhance network stability. While 1st and 2nd stages are formulated as non-linear programming problems, the 3rd stage is formulated as a mixed-integer non-linear problem. The problems are optimized using the CPLEX solver in the general algebraic modeling system (GAMS) environment. The lower control level is implemented by following a few rules that adjust the local Q(V) characteristics embedded in the power electronics interfaced devices. The obtained results exhibit that the devised framework not only helps in voltage regulation but also the EV owners and the EVA. Later, the profit earned by EVAs is computed for slow and fast charging schemes.
Control of a PV-Wind Based DC Microgrid with Hybrid Energy Storage System Using Lyapunov Approach and Sliding Mode Control
Thomas T., Mishra M.K., Kumar C., Liserre M.
Article, IEEE Transactions on Industry Applications, 2024, DOI Link
View abstract ⏷
This paper focuses on the control techniques implemented on a PV-wind based standalone DC microgrid with hybrid storage system. An Enhanced Exponential Reaching Law (EERL) based sliding mode control (SMC) is applied for extraction of maximum power in a Permanent Magnet Synchronous Generator (PMSG) based wind energy system. This reaching law based SMC tracks current reference from the optimum torque MPPT algorithm during different wind speeds and load variations and has a good dynamic response. A combination of battery and supercapacitor is used as the hybrid storage system for providing reliable and continuous power to the load. The supercapacitor absorbs the transient components during disturbances and helps in improving the life of battery. A control method based on the Lyapunov function, which can ensure global asymptotic stability is implemented for the bidirectional converter of battery and supercapacitor. The proposed method maintains the DC link voltage constant during solar, wind and load variations. A detailed analysis of the two control laws is presented. The superiority and efficacy of the proposed control strategies are validated on the DC microgrid system during different operating conditions by simulation studies and by developing an experimental test bench.
Net Load Forecast Error Compensation for Peak Shaving in a Grid-Connected PV Storage System
Manojkumar R., Kumar C., Ganguly S., Catalao J.P.S.
Article, IEEE Transactions on Power Systems, 2024, DOI Link
View abstract ⏷
In modern power systems, it is important to compensate net load forecast errors which are caused due to variability and uncertainty of load and renewable energy source powers for improving the stability and reliability. Super capacitor (SC) is a well suited component for compensating forecast error due to its power and energy density characteristics. In this article, a novel method is proposed for net load forecast error compensation through SC application. The proposed method is simple and general which can be used at industry scale while implementing the energy management applications. In order to test the performance of the proposed method, a grid-connected photovoltaic storage system is considered. The forecast error in load/PV powers is compensated while limiting both grid demand and feed-in powers to their optimal limits. Battery energy storage system charge/discharge schedules are controlled by a rule-based peak shaving method to minimize the day-ahead average peak demand of the system. For controlling SC charge/discharge schedules, the proposed net load forecast error compensation method is used. It is observed that the peak demand and feed-in powers are reduced significantly with the proposed method as compared with the case when there is no net load forecast error compensation.
AC Short-Circuit Fault Detection and Isolation in Islanded Microgrid
Conference paper, Proceedings of the International Conference on Power Electronics, Drives, and Energy Systems for Industrial Growth, PEDES, 2024, DOI Link
View abstract ⏷
This paper investigates AC short-circuit fault detection and isolation technique in islanded microgrid having grid-forming (GFM) and grid-following (GFL) converters. The study focuses on the impact of AC side faults on the DC side performance of the converters, analyzed through mathematical analysis and simulations. Asymmetrical faults induce second-order harmonics in the DC current, causing oscillations in it. During symmetrical faults, the DC side current experiences higher fault currents compared to an asymmetrical fault without oscillations. In case of GFL converter as operating in current control mode (CCM), it does not contribute to fault current, whereas the GFM converter handles the fault current independently due to voltage control mode (VCM). These results emphasize the potential for efficiently detecting and quickly isolating AC side faults using DC side current measurements, which simplifies fault management and enhances system reliability and resilience.
Development of FPGA-based Interface Card for Power Electronic Converter Control
Conference paper, Proceedings of the International Conference on Power Electronics, Drives, and Energy Systems for Industrial Growth, PEDES, 2024, DOI Link
View abstract ⏷
Multilevel topologies, back-to-back converter systems, solid-state transformers, etc., require many analogue signals for their control. To implement digital control in these systems, a custom interface circuit for digital processors needs to be developed. This paper presents a systematic design and development of an interface card for the digital control of such power elec-tronic converters. The proposed design consists of two daughter cards (signal conditioning card and analogue-to-digital converter (ADC) card) connected to Zedboard development board. An ADC driver is developed and discussed as a state machine. A total of 40 analogue signal intakes is provided, along with 40 general-purpose input/output (GPIO) pins and communication features like serial peripheral interface (SPI), campus area network (CAN), and universal asynchronous receiver/transmitter (UART). The ADC card printed circuit board (PCB) is simulated in Ansys SIwave for direct current internal resistance (DCIR) analysis. The signal conditioning circuit is analysed with a frequency response that considers the circuit parasitic. Lastly, hardware results are showcased, verifying the proposed solution.
Dual Loop based Andronov-Hopf Oscillator Control of Grid-Connected Photovoltaic Systems
Conference paper, IECON Proceedings (Industrial Electronics Conference), 2024, DOI Link
View abstract ⏷
The grid-connected dc-ac converters encounter significant challenges in maintaining stable operation on both dc and ac sides, especially with solar photovoltaic (PV) at the dc-link. The grid-forming (GFM) converter is nowadays preferred due to its capability to establish and maintain grid stability and synchronization, even under weak grid conditions. This paper describes a dual-loop control structure that cascades Andronov-Hopf oscillator (AHO)-based virtual oscillator (VO) control with dual voltage and current control to directly address voltage variations and control the converter output variables. Additionally, the power synchronization loop of VO control incorporates dc-link dynamics to facilitate maximum power point tracking (MPPT)-based PV systems. The simulation results show that the proposed controller enables PV to dispatch power at MPPT while providing stable synchronization at the ac side. The performance of the controller is further examined by adjusting the internal VO parameter for current gain and the external grid’s R/X ratios.
Inertia Synthesis for AHO Controlled Converters in Smart Transformer Based Distribution Systems
Conference paper, Proceedings of the International Conference on Power Electronics, Drives, and Energy Systems for Industrial Growth, PEDES, 2024, DOI Link
View abstract ⏷
The smart transformer (ST)-based low-voltage distribution systems have lower inertia, primarily due to the lack of rotating machines. This characteristic becomes critical when integrating high levels of renewable-based distributed generation (DG) units. The grid-forming (GFM) control mode in low voltage (LV) converters can apply either virtual synchronous generator or, droop control to coordinate with DGs. However, these control strategies are based on the phasor-domain, and synchronous steady-state needs to be well defined. On the other hand, the virtual oscillator (VO) control is a time-domain based decentralized GFM converter control technique and globally asymptotic stable. In this paper, a virtual inertia (VI)-VO control equipped with a proportional-derivative (PD) controller is pro-posed to generate a response comparable to that of a synchronous generator (SG) inertia. The impact of adjusting the equivalent VO control inertia constant is evaluated through simulation in MATLAB/Simulink software. The simulation and experimental results demonstrate that the proposed VI-VO control enhances frequency characteristics like the rate of change of frequency (RoCoF) and frequency nadir.
Volt/Var Control of Smart Transformer fed Active Distribution Networks
Dutta A., Ganguly S., Kumar C.
Conference paper, Proceedings of the International Conference on Power Electronics, Drives, and Energy Systems for Industrial Growth, PEDES, 2024, DOI Link
View abstract ⏷
In this article, model predictive based centralized control strategy is proposed to manage voltage variations and line congestions in smart transformer (ST) fed distribution networks with electric vehicles (EVs) and photovoltaic (PV) generators. ST is a power electronics-based transformer that exhibits intelligent features in control and communication fields. The proposed control scheme deals in coordinating the fast power electronics interfaced devices, such as EVs, ST and PVs in the low voltage (LV) side to maintain voltages as well as line congestions. The ST provides the voltage control in the LV side by setting the voltage reference at the source of the feeder in a similar manner a conventional transformer with on-load tap changers. Simulations are performed in a 38-bus distribution network to validate the efficacy of the proposed approach.
A Finite Control Set Based Model Predictive Control for Reducing Inductor Current Ripple in Dual Active Bridge Converter
Meikap S., Kumar C., Carnielutti F., Rodriguez J.
Conference paper, Proceedings of the International Conference on Power Electronics, Drives, and Energy Systems for Industrial Growth, PEDES, 2024, DOI Link
View abstract ⏷
Inductor current ripple in a dual active bridge (DAB) converter increases voltage stress, core loss, and electromagnetic interference (EMI). This paper proposes a finite control set-based model predictive controller (FCS-MPC) for reducing inductor current ripple in a DAB converter system. The FCS-MPC reduces the inductor current ripple by controlling the primary side switching with a sinusoidal reference current without affecting the power transfer requirement. It has several benefits like no modulator requirement, faster response, better transient and steady-state performance.
A Multiport Battery Swapping Station Based on a Hybrid Modular Converter: Its Dynamic Control Strategy
Kumar C., Rath I.C., Patro S.K., Kumar V.
Conference paper, Conference Record - IAS Annual Meeting (IEEE Industry Applications Society), 2024, DOI Link
View abstract ⏷
With the rapid growth of electric vehicles (EVs) on the roads, the demand for efficient charging infrastructure has become paramount. The modular multilevel based converters stand out as a promising technology for multiport EV chargers. This article proposes a hybrid modular converter with a dynamic control strategy for multiport battery swapping station. Each phase of this converter topology has two sections, series switch parts and wave orientation portion (WOP). The series switch parts are connected to grid via transformer to extract energy for charging, whereas each WOP provides the multiple charging ports. This article uses a dynamic control methodology to balance the voltage of WOP during the charging process, which eliminates the DC-DC converters requirements as the batteries can be directly connected to WOPs. Thus, a charging station with optimize footprint and initial investment can be realized. The working principle and the developed dynamic control mechanism of proposed hybrid modular converter are verified using a threephase seven level experimental setup.
Coded Power Transfer for Power Electronic Converter System
Naleo V., Malviya H., Anandh N., Kumar C.
Conference paper, Proceedings of the International Conference on Power Electronics, Drives, and Energy Systems for Industrial Growth, PEDES, 2024, DOI Link
View abstract ⏷
Information exchange between the load side and the source side allows the power electronic system to adjust its operation to match the load requirements dynamically. This paper presents a mechanism for the transfer of power and data between the load and the source sides of the power electronic system. The system utilizes the coded information in the switching signals adopting coded power transfer. The data to be transmitted is converted into a binary fixed point number and is superimposed on the switched voltage to transfer the information. The coded power transfer is implemented on a buck converter system. The conversion of data from the analog domain to the digital domain and vice versa is explored. The simulation results are obtained from MATLAB/Simulink software and Hardware-in-loop validating the sequential transmission of data and power.
MPC Based Phase Angle Adjustment for Optimal Power Transfer in Neutral Point Clamped Dual Active Bridge Converter
Meikap S., Gopal R., Kumar C., Rodriguez J.
Conference paper, Proceedings of the International Conference on Power Electronics, Drives, and Energy Systems for Industrial Growth, PEDES, 2024, DOI Link
View abstract ⏷
For high-voltage applications, neutral point clamped-based dual active bridge (NPC-DAB) converters are commonly used. In literature, different fixed phase shift control methods like double phase shift control (DPS), triple phase shift control (TPS), etc., are used to reduce losses in NPC-DAB converter. In this paper, a variable phase shift method is proposed to reduce the losses in the converter. This variable phase shift angle is obtained by utilizing a power loss minimization function in a model predictive controller (MPC). The simulation result shows that MPC based variable phase shift control reduces power loss and improves transient performance in the NPC-DAB system in comparison to PI control based fixed phase shift control.
Model Predictive Control of Solar PV and Battery Converters Using Droop Control
Kumar D., Meikap S., Kumar C., Carnielutti F., Rodriguez J.
Conference paper, Proceedings of the International Conference on Power Electronics, Drives, and Energy Systems for Industrial Growth, PEDES, 2024, DOI Link
View abstract ⏷
This paper presents a droop control based finite control set model predictive control (FCS-MPC) of a hybrid energy system. The hybrid energy system consists of a solar photovoltaic (PV) and a battery energy storage system (BESS) connected to a DC bus. The droop control is designed to control DC bus voltage depending on the state of charge (SoC) of BESS and load. When the BESS is not fully charged, the BESS converter regulates the DC bus voltage, while the PV converter operates at maximum power point tracking (MPPT). In case of BESS is fully charged and MPPT power is greater than load power, the PV converter regulates the DC bus voltage considering I-V droop control. The proposed method provides good transient response to load power variation for single stage DC-DC converter. The simulation studies are performed in MATLAB/Simulink to show the effectiveness of the proposed method.
Modular Hybrid Series-Parallel DC-DC Converter for HVDC to MVDC Applications
Kumar C., Tandi P., Kumar L., Yadav M.M., Singh A.K., Patro S.K.
Conference paper, Proceedings of the International Conference on Power Electronics, Drives, and Energy Systems for Industrial Growth, PEDES, 2024, DOI Link
View abstract ⏷
The benefits of high voltage direct Current (HVDC) technology have made it indispensable for power systems. They consist of lower losses, simpler asynchronous grid connections, better controllability, increased system availability, and a decrease in short-circuit currents. This article introduces a new modular hybrid series-parallel DC-DC Converter (MHSPDC) topology designed for efficient power transfer in HVDC- medium voltage direct current (MVDC) applications. Each phase of a series DC-AC structure and a parallel AC-DC structure, interconnected by a single-phase isolated transformer. This new topology offers significant reductions in footprint and initial investment costs while enhancing converter efficiency. The article provides a brief description of the circuit configuration, operational principles of the converter and mathematical analysis of capacitor sizing used in the converter topology. The MATLAB/PSCAD simulation software is utilized to validate the novel configuration. During the simulation, a phase disposition technique is employed as PWM for converter switching.
Empowering Employee Wellness and Building Resilience in Demanding Work Settings Through Predictive Analytics
Dikshit S., Grover Y., Shukla P., Mishra A., Sahu Y., Kumar C., Gupta M.
Article, EAI Endorsed Transactions on Internet of Things, 2024, DOI Link
View abstract ⏷
In today's fast-paced and competitive corporate landscape, the well-being of employees is paramount for sustained success. This paper explores the transformative potential of predictive analytics in cultivating a healthier, more resilient workforce within high-pressure work environments. The title "Empowering Employee Wellness and Building Resilience in Demanding Work Settings Through Predictive Analytics" encapsulates our objective of harnessing data-driven insights to mitigate the negative effects of high-pressure work settings and foster an environment where employees thrive. Through an in-depth examination of predictive analytics tools and methodologies, this study offers a roadmap for organizations to proactively identify stressors, predict burnout risks, and implement targeted interventions. By collecting and analysing relevant data, employers can tailor support systems, optimize workloads, and implement mindfulness programs that enhance employee well-being. Moreover, organizations can better adapt to change, maintain workforce continuity, and drive productivity by fostering resilience through predictive insights. This research bridges the gap between data science and human resources, offering a holistic approach to employee wellness and resilience-building. By leveraging predictive analytics, companies can create a culture of care where employees feel supported, empowered, and more capable of surviving and thriving in high-pressure work environments.
Stabilization of Smart Transformer Based Islanded Meshed Hybrid Microgrid during Electric Vehicle Charging Transients
Das D., Kumar C., Liserre M.
Article, IEEE Journal of Emerging and Selected Topics in Industrial Electronics, 2023, DOI Link
View abstract ⏷
Smart transformer (ST)-based meshed hybrid microgrid is an attractive solution for interfacing various energy sources and loads, while achieving improved power management features. In the islanded operation of such ST-based meshed grid, battery energy storage system (BESS) maintains the low voltage (LV) dc link voltage and acts like a slack bus. During sudden changes in load like charging of electric vehicles (EVs), such a system can become unstable due to slower system response owing to right half plane zero, which is inherently present in BESS converters. This article proposes a method of stabilizing an ST-based islanded meshed hybrid microgrid during transients arising from EV charging. To maintain the system stability during such load transients, the meshed nature of the system is exploited by controlling the LVac voltage using ST LV converter operating in grid forming mode. This in turn enables a control of the total load in the LVac grid. The proposed scheme provides a simple yet effective method to stabilize meshed islanded system in spite of slower system dynamics. The design and stability analysis of the converters are presented to study the system performance with the proposed method. Simulation and experimental results verify the proposed control scheme.
Rule-Based Peak Shaving Using Master-Slave Level Optimization in a Diesel Generator Supplied Microgrid
Manojkumar R., Kumar C., Ganguly S., Gooi H.B., Mekhilef S., Catalao J.P.S.
Article, IEEE Transactions on Power Systems, 2023, DOI Link
View abstract ⏷
This paper proposes a rule-based peak shaving method using master-slave level optimization and presents its impact on an isolated diesel generator (DG) supplied microgrid. The DG is connected to low voltage (LV) ac bus through a back-to-back converter. This DG supplies power to a modified CIGRE residential distribution system which consists of residential loads and renewable energy sources (RESs). In such a system the fuel consumption of DG not only depends on the LV ac bus power requirement but also on its rated power. The rated power of DG can be reduced through the peak shaving application. In this scenario, a battery energy storage system (BESS) is connected at dc bus of the back-to-back converter for the peak shaving of DG power. The rule-based peak shaving method is proposed for determining BESS charge/discharge schedules considering the day-ahead LV ac bus powers over a day as inputs. For that firstly the LV ac bus powers are optimally obtained using a slave level optimization. In order to obtain the optimal peak DG power a master level optimization is used which determines the optimal control inputs for the rule-based control. The proposed peak shaving control method is tested in MATLAB.
Model Predictive Control of Isolated Three-Phase Four-Wire Grid Forming Converter
Conference paper, 2023 11th National Power Electronics Conference, NPEC 2023, 2023, DOI Link
View abstract ⏷
This paper presents finite control set model predictive control (FCS-MPC) for an isolated three-phase four-wire (3P4W) grid forming converter (GFC). The GFC uses an inductor-capacitor (LC) filter at the load terminal. The objectives are to 1) supply power to balance loads and non-linear loads, 2) supply power to unbalance loads, and 3) use a single control loop to regulate the GFC output voltage. The simulation results are presented to verify the features of isolated GFC.
Smart Transformer Based Ship Microgrid System
Conference paper, 2023 11th National Power Electronics Conference, NPEC 2023, 2023, DOI Link
View abstract ⏷
Over the years, all-electric-ships (AES) have gained importance due to the reduced losses and superior features as compared to conventional ships. However, several power conversion stages are needed in this type of configuration which results in added system complexity. Propulsion loads are the highest power consuming loads with considerable amount of power electronic interfaces. This paper proposes the incorporation of smart transformer (ST) into a ship microgrid in place of the conventional bulky power transformers. Such a system enables saving of space as well as availability of two dc links to integrate renewable energy sources and energy storage systems. Further, it eliminates the need of additional power converters such as static compensator (STATCOMs), power factor correction devices, capacitor, etc. Moreover, as the service loads are supplied power through power electronic interfaces, disturbances appearing from propeller load variations do not appear in the ships distribution system. Simulation results validate the operation of proposed ST based ship microgrid.
Virtual Oscillator Control of Smart Transformer based Meshed Low Voltage Distribution Grid
Conference paper, 2023 IEEE Energy Conversion Congress and Exposition, ECCE 2023, 2023, DOI Link
View abstract ⏷
Distributed generations (DGs) and electric vehicle charging stations (EVCSs) are continuously increasing in the distribution system. These lead to voltage and frequency violations, lower inertia, poor power quality, etc. Smart transformer (ST) with meshed network of distribution lines is considered as an effective solution for improving the performance, stability and flexibility in power flow. However, it requires effective and precise control of power converters. This paper analyzes the performance of an autonomous decentralized virtual oscillator (VO) control strategy for dc-ac converters in ST based meshed distribution system. Moreover, the comparison of time domain-based VO with phasor domain-based droop controlled converters is carried out. Simulation and experimental results are presented to show their active and reactive power-sharing capability, voltage, and frequency at buses during steady state and transient conditions.
Multiport DC Fast EV Charger Based on Modular Multilevel Converter and Quad-Active Bridge
Conference paper, 2023 11th National Power Electronics Conference, NPEC 2023, 2023, DOI Link
View abstract ⏷
This paper presents a multiport DC fast electric vehicle (EV) charger based on a modular multi-level converter (MMC) and a quadruple active bridge (QAB). An adaptive dc link voltage regulator is developed for MMC to reject parameter uncertainties (including change in load). A proportional-integral (PI) based current control scheme is developed to track reference currents for MMC's unity power factor (UPF) operation. MMC's sub-module (SM) switching is provided with sorting scheme-based capacitor balancing with level-shifted pulse width modulation (PWM). Three fast charging ports are provided; each can charge an electric vehicle (EV) as a standalone leve1-3 DC charger by QAB converter. Separate control architectures are designed for constant current (CC)/constant voltage (CV) for each charging port of QAB. The simulation is done in Matlab, and the results are shown for a 3.3 kV grid with three identical 200 Ah, 700 V Li-ion batteries with different state-of-charges (SOCs).
An NPC Based Triple Active Bridge Isolated Converter for Fast Onboard Battery Charger for All Electric Ship
Conference paper, 2023 11th National Power Electronics Conference, NPEC 2023, 2023, DOI Link
View abstract ⏷
The rapid evolution of electric propulsion technologies has led to a paradigm shift in the maritime industry, with all electric ships emerging as a viable and environmental-friendly alternative to conventional vessels. Electric ships, powered by energy-dense battery systems, offer reduced emissions, lower operating costs, and enhanced operational efficiency. However, the successful integration of electric ships into the maritime ecosystem necessitates a comprehensive charging infrastructure. This paper explores the critical need for high power battery chargers in electric ships. A neutral-point-clamped (NPC) based triple active bridge fault tolerant converter is designed and operated as onboard battery charger with isolation, lower voltage stress, better controllability, etc. Extensive simulation are shown to validate the operation.
UPS Operation of Smart Transformer Fed Triple-Active Bridge Converter for Data Centres
Anandh N., Das D., Kumar C.
Conference paper, 2023 11th National Power Electronics Conference, NPEC 2023, 2023, DOI Link
View abstract ⏷
The vigorous demand for big data, cloud computing and the development of 5G technology forced the data centres to grow consistently. The power supply system of data centre requires highly efficient and reliable power to maintain the regular operation of information technology (IT) equipment's. In this paper, the uninterruptible power supply (UPS) operation of smart transformer (ST) fed triple-active bridge (TAB) converter for continuity of power supply in data centres is explored. The ST fed TAB converter offers quality ac/dc powers at different voltage levels, provides backup power, and ensures reliability of power distribution in data centres. Renewable energy sources (RES) such as solar, wind, and battery energy storage systems (BESS) are the integral elements in UPS operation. The PSCAD software is utilized to simulate the system and verify its functionality in UPS mode, guaranteeing a continuous power supply to data centres.
Power Management of a Smart Transformer based Ship Microgrid
Dutta A., Manojkumar R., Kumar C.
Conference paper, 2023 11th National Power Electronics Conference, NPEC 2023, 2023, DOI Link
View abstract ⏷
With extensive number of power electronically interfaced loads and generations, ship microgrids exhibit similar traits as terrestrial microgrids. The replacement of conventional power transformers with smart transformers in ship microgrid adds flexibility to the system. However, the presence of large number of smart power converters in the ship power systems introduce power quality problems, voltage and frequency violations, etc. Moreover, large dynamic loads in ships augment the challenges for ship power operators. This necessitates a proper control and power management strategy for a ship microgrid. This paper presents a power management strategy for a diesel generator driven smart transformer based ship microgrid. The proposed power management strategy aims to reduce the power drawn from diesel generator by minimizing the LVAC bus power, while maintaining the bus voltages within desired limits. Simulation results validate the effectiveness of the proposed strategy.
Operation of a New Fault-Tolerant Dual Active Bridge Converter
Meikap S., Malviya H., Kumar C.
Conference paper, 2023 IEEE Energy Conversion Congress and Exposition, ECCE 2023, 2023, DOI Link
View abstract ⏷
The advancement of dc-dc converter technology has been greatly aided by the adoption of renewable energy sources, uninterruptible power supplies, and energy storage devices. There is a requirement for isolated dc-dc converter systems that offer isolation and quick power transfer between different dc bus systems due to the growth of distributed generation and dc loads. Dual active bridge (DAB) is one of the most commonly used isolated dc-dc converters. However, its primary drawback is that it does not function when switches fail. This led to development of different configuration of DAB for fault tolerance. Several additional components are required for fault tolerant DAB which increases control complexity and losses. In this paper, a simple capacitor integrated circuit breaker (CICB) system is proposed to convert each active bridge of DAB into a fault tolerant system. The fault tolerant DAB system operates on single phase shift (SPS) control throughout its operation. Simulation and experimental tests are carried out to verify the theoretical analysis.
LCL-LCL Topology based Resonant Inductive Wireless Power Transfer System
Gaurav S., Kumar C., Meena A.
Conference paper, 2023 11th National Power Electronics Conference, NPEC 2023, 2023, DOI Link
View abstract ⏷
The wireless power transfer (WPT) for electric vehicle (EV) charging has received significant attention due to several advantages, including ease of use, safety, low maintenance requirements, weather resistance, etc. This paper presents control, design, and prototype configuration of resonant inductive LCL-LCL topology based WPT system. The estimation of values and ratings of components for individual sections based on the designed parameters are explained in detail. The experimental results verify the design and show the effectiveness of WPT system. The performance of coil coupling setup and whole system is found by calculating the efficiency at different voltage levels.
Coil Coupling Design for Resonant Inductive Wireless Power Transfer System
Gaurav S., Kumar C., Meena A.
Conference paper, 2023 11th National Power Electronics Conference, NPEC 2023, 2023, DOI Link
View abstract ⏷
The coil coupling structure in wireless power transfer (WPT) system plays a crucial role when power is transferred by magnetic coupling. The coupling coefficient between linked coils and resistive coil losses determine the efficiency and power transfer of WPT system. In this paper, the commonly used coil coupling shapes, including helix and spiral, are compared, and spiral coil structure is developed for EV charging. The inductance characteristics of the coil structure are measured and compared with the theoretically calculated values. The developed spiral coil coupling system is tested for different heights and misalignment. Moreover, the simulations of resonant inductive WPT system with series-series (SS) and LCL-LCL topologies are done in MATLAB/Simulink environment. The LCL-LCL topology aids in mitigating harmonic distortions and improving the power quality of the WPT system, by enabling effective filtering and resonance establishment.
Review of Voltage Limit and Transient Voltage Stability Criteria for Power System Planning
Kumar M., Kumar C., Saxena R.K.
Conference paper, 2023 3rd International Conference on Emerging Frontiers in Electrical and Electronic Technologies, ICEFEET 2023, 2023, DOI Link
View abstract ⏷
Voltage criteria in power systems during steady state and dynamic conditions are important for safe and secure grid operation and ensuring system planning with margin for security. This paper reviews and compares voltage stability criteria-specifically, voltage limit and transient voltage stability criteria across different countries and utilities used for power system planning and operation including India. Examining their implications for power system planning and operation, the study explores how criteria selection is influenced by regulatory frameworks, grid characteristics, and regional needs. By analyzing diverse approaches, the paper identifies commonalities and variations in voltage stability practices across the globe. It offers recommendations for tailoring criteria to specific contexts, emphasizing a balanced consideration of steady-state and transient stability. The research advances understanding of global voltage stability assessment methodologies, enabling better-informed decisions for ensuring grid reliability and sustainable energy delivery.
An Arduino Based Modular Battery Management System for Protection and Real Time Monitoring of Lithium-Ion Cell
Meikap S., Kumar N., Kumar C.
Conference paper, 2023 11th National Power Electronics Conference, NPEC 2023, 2023, DOI Link
View abstract ⏷
Battery management systems (BMS) are widely used for proper protection and utilization of battery systems. In this paper, a modular BMS circuit is proposed for the design of modular battery stacks that can be reconfigured depending upon utilization. The real-time evaluation is carried out using four local modules and one central module. An Arduino nano with an analog-digital converter (ADC) multiplexer and voltage divider circuit is used as central module in the BMS system. The BMS voltage measurement accuracy is evaluated with the measured value. The state of charge (SOC) measurement technique is developed to calculate the SOC of each cell. A protection circuit is designed for under-voltage, over-voltage, and short-circuit in battery cells. The circuit also provides passive cell balancing. The hardware results verify the operation of the circuit as well as the cell balancing in the battery cells during the charging and discharging cycle.
Performance Enhancement of Quad Active Bridge Converter During Faults
Meikap S., Malviya H., Kumar C.
Conference paper, IECON Proceedings (Industrial Electronics Conference), 2023, DOI Link
View abstract ⏷
Renewable energy generation, uninterruptible power supplies, and energy storage systems have served as crucial factors in the advancement of dc-dc converter technology. With the rise of distributed generation and dc loads, there is a need for multi-port converter system that provides isolation and fast power transfer between different dc bus systems. For a multi-port converter system to become popular, it needs to have low losses, faster response, and fault tolerance capability. Quad active bridge (QAB) is a type of multi-active bridge system that can cater to such needs, but it does not have protection from power electronics switch faults. In this paper, a fault-tolerant QAB with minimal passive components is designed. A key advantage of the designed system is that the same control technique is used throughout the operation. This reduces the complexity of controller design. Simulation results confirm the proposed technique for open circuit and short circuit fault condition.
Operation and Control of Modular Multilevel DC-DC Converter for EV Charging Application
Sahu S.K., Prasoon S., Gaurav S., Kumar C.
Conference paper, 2023 11th National Power Electronics Conference, NPEC 2023, 2023, DOI Link
View abstract ⏷
This paper presents a self balanced modular multilevel dc-dc converter (MMDC) based on the conventional buck converter topology, where both switches are replaced by capacitor clamped submodules (SMs). This converter achieves a significant reduction in input voltage through a high-voltage step-down ratio, which is determined by the number of SMs. The phase shifted carrier pulse width modulation (PSC-PWM) technique is used to control the switching state of SMs such that there is a constant number of SMs supporting the input voltage at any time. The converter exhibits an inherent capability to balance the voltages of the SM capacitors without the need for additional complex balancing control techniques. The structure of the two level high step down ratio (5:1) MMDC, along with its operating mode analysis and parameter design, are presented in this paper. The effectiveness of the MMDC is validated through the simulation and experimental results.
Hardware Design and Development of Modular Multilevel Converter
Mayank K., Verma A., Meikap S., Hrishikesan V.M., Kumar C.
Conference paper, CPE-POWERENG 2023 - 17th IEEE International Conference on Compatibility, Power Electronics and Power Engineering, 2023, DOI Link
View abstract ⏷
Modular multi-level converter (MMC) is a popular multi-level converter configuration due to its various features such as ease of scalability, modularity, and low voltage and current rating demand for the power switches. This paper presents the development and implementation of hardware prototype of MMC as a grid forming inverter. An MMC prototype is developed having three sub-modules in an arm, which can be configured as either half bridge-based sub-module or full bridge-based sub-module. Design of various circuits and sizing of various components are carried out for the MMC setup. All the hardware related design and control technique are discussed. Lastly, hardware results for operation of MMC as grid forming inverter are presented.
Design and fabrication of three direction dumping mechanism in trucks
Sharma S.L., Agrawal A.P., Kumar C.
Conference paper, Materials Today: Proceedings, 2022, DOI Link
View abstract ⏷
This study aims to overcome difficulties in loading and unloading material in a single dumping mechanism in industries. The delivery of material is not a difficult task in recreational areas but in certain places where space is less for the trailer to deliver, which could be difficult for the truck driver. To control the difficulty of the truck pilot, an initiative of designing and fabricating three directional discarding mechanism in trucks can deliver the material in three directions such as in the left, right, and as a usual rear region. A hydraulic pneumatic cylinder is mounted in the damming mechanism system to lift the trolley in a particular direction & position. For tilting the trolley wagon in identified direction, locking pins in the trolley wagon are hardened to lock. This paper mainly focuses on the fabrication with design calculations of locking mechanisms controlled by directional control. This mechanism saves energy and time to load and unload material without difficulties.
Retention Problem Free High Density 4T SRAM cell with Adaptive Body Bias in 18nm FD-SOI
Kumar C., Kumar R., Grove A., Chatterjee S., Dhori K.J., Rawat H.
Conference paper, Proceedings - 2022 35th International Conference on VLSI Design, VLSID 2022 - held concurrently with 2022 21st International Conference on Embedded Systems, ES 2022, 2022, DOI Link
View abstract ⏷
Area scaling of 6T SRAM cells has stagnated in advanced technology nodes [1]. The conventional 6T SRAM bitcell is bulky because of two pull-down NMOSs, which are sized to ensure cell stability. In this work, we present alternative 4T SRAM and 6T SRAM cells that eliminate these pull-down transistors. A 4T SRAM cell, so designed, is 10-13% denser than a 6T bitcell. 4T SRAM cells typically suffer from low data retention time and need to be refreshed regularly. We apply Adaptive Body Bias to alleviate the retention problem. In 18nm FD-SOI technology, the retention problem is completely mitigated, and leakage is reduced by 6× times that of 6T SRAM cells.
India’s Kolkata Section and Guwahati Subsection Inaugurate the IEEE PELS Joint Section Chapter
Article, IEEE Power Electronics Magazine, 2022, DOI Link
Coordinated Volt/Var Control of PV and EV Interfaced Active Distribution Networks Based on Dual-Stage Model Predictive Control
Dutta A., Ganguly S., Kumar C.
Article, IEEE Systems Journal, 2022, DOI Link
View abstract ⏷
This article presents a dual-stage coordinated control approach for voltage regulation and congestion management of active distribution networks (ADN) in the presence of photovoltaic (PV) generators and electric vehicle stations (EVS). The proposed scheme operates on rule-based model predictive control (RBMPC) to optimally manage the settings of the regulating devices, i.e., on-load tap changer (OLTC), distribution static synchronous compensator (DSTATCOM), PV generators, and EV inverters that possess different temporal characteristics. The first (hourly time-scale) and the second (one-minute time-scale) stages of the dual-stage coordinated control mechanism are designed to correct the long-term and short-term voltage fluctuations, respectively. The objectives of the proposed approach are to minimize the number of OLTC operations (first stage) and changes in set-points of PV and EV inverters, and DSTATCOM (second stage) in addition to minimization of slack variables, energy loss, and voltage error at EV stations. In both the stages, predefined rules are set for MPC to optimize different objectives on the basis of the magnitudes of bus voltages. Simulations are performed on 33-bus and 38-bus distribution networks to test the efficacy of the control approach. It is observed that the proposed approach could mitigate the voltage variations as well as line congestion for different scenarios.
Coordinated control scheme for EV charging and volt/var devices scheduling to regulate voltages of active distribution networks
Dutta A., Ganguly S., Kumar C.
Article, Sustainable Energy, Grids and Networks, 2022, DOI Link
View abstract ⏷
This paper proposes a three-stage model predictive control (MPC)-based centralized coordinated approach to schedule charging of electric vehicles (EV) and volt/var (VV) devices. The approach aims at maintaining bus voltage magnitudes and state-of-charge (SOC) of EV battery within desired limits with minimal usage of control resources and cost of electricity consumption. The first stage determines the optimal operating points of traditional discrete control devices on an hourly basis. The second stage dispatches the optimal set-points of power electronics interfaced fast devices [photovoltaic (PV) and EV inverters] every one minute. The third stage schedules charging/discharging of EV half-hourly with respect to the real-time electricity price. Furthermore, several rules are formulated to adjust the local volt/var curve of PV and EV inverters according to the voltage magnitudes. The combined central and local control approach ensures that EVs attain the desired SOC at the time of their departure from the charging station without violating the voltage limits. The proposed control approach is tested in a 33-bus distribution network and 38-bus distribution network with different operating conditions. Simulation results depict that the performance of the proposed control approach is better than uncoordinated charging in terms of reduced voltage deviations, energy loss, and control resources utilization.
An MVDC-Based Meshed Hybrid Microgrid Enabled Using Smart Transformers
Hrishikesan V.M., Kumar C., Liserre M.
Article, IEEE Transactions on Industrial Electronics, 2022, DOI Link
View abstract ⏷
Decentralized integration of distributed generation units and loads is increasing in the modern distribution grid. Maintaining the power flow and power quality within their accepted limits is a challenging task. The formation of meshed hybrid microgrids is an effective method to improve the power system. The smart transformer (ST) is a promising solution to establish meshed hybrid microgrids in the distribution system. This article analyzes the performance of an ST-based meshed hybrid microgrid interconnected to the main grid feeder through medium voltage (MV) dc-link of a second ST. The coordinated operation of interconnected ST system is proposed to explore the features of the configuration. During normal operation, the MVdc bus voltage is controlled by one ST, and this reduces the complexity of the overall control. The main grid and microgrid MVac source failure and converter fault conditions are explored to analyze the reliability of the proposed microgrid structure. Moreover, the reactive power support capability and active power losses for the proposed system are compared with the existing solutions. Simulation and experimental results are presented to show the operation of the proposed system.
Optimal Demand Response in a Residential PV Storage System Using Energy Pricing Limits
Manojkumar R., Kumar C., Ganguly S.
Article, IEEE Transactions on Industrial Informatics, 2022, DOI Link
View abstract ⏷
This article presents an optimal demand response (DR) control for a residential photovoltaic (PV) storage system using energy pricing limits. Unlike the existing literature, both energy buying and selling prices are considered in DR application for reducing the energy cost of the system. A method for determining buying price and selling price limits of the day using day-ahead predictions of energy price, load demand, and PV power profiles is proposed. To further reduce the energy cost of the system subbuying price limit is considered. A rule-based DR control for minimizing the energy cost of the system is proposed. The rules are formulated such that energy buying price and selling prices are limited to their corresponding price limits of the day with the flexible day-to-day management of battery energy storage system. For obtaining optimal results with rule-based control, required control inputs are determined optimally using genetic algorithm. The proposed method is tested in MATLAB. It is observed that energy cost savings of 34.09% and 5.4% are obtained on the day of more PV energy availability and less PV energy availability, respectively, based on the day-ahead operation. Further, the impact of uncertainties on the proposed DR control is discussed for real-time operation of the system.
Coordinated Control of EV Charging Stations in Smart Transformer based Microgrid
Conference paper, 2022 22nd National Power Systems Conference, NPSC 2022, 2022, DOI Link
View abstract ⏷
This paper presents coordinated control scheme of electric vehicle charging stations (EVCSs) in smart transformer (ST) based microgrid. The microgrid is connected to the main grid through ST. Here, ST low voltage (LV) ac side converter is operating on the droop-control method. Battery energy storage system (BESS) and photovoltaic (PV) are connected to LVac line through droop-controlled converters. Two levels of hierarchical control structure have been implemented here: primary control and secondary control. EVCS connected at the load bus is used as the controllable unit in microgrid, which can regulate the voltage and frequency at load bus. Moreover, EVCS supports the microgrid with reactive power by varying their charging power. The secondary control at the microgrid centralised controller (MGCC) sends compensation signals to all the control units of droop-controlled converters and EVCS using the low bandwidth communication link. Simulation results show that the microgrid provides power at nominal voltage and frequency using secondary compensation signals. Along with controllable charging, EV supports reactive power as the voltage deviation at load bus goes beyond minimum threshold limit. The results are verified using the MATLAB/Simulink software.
Model Predictive Control of Bi-directional dc-dc Converter for Battery Charger Application
Conference paper, 2022 22nd National Power Systems Conference, NPSC 2022, 2022, DOI Link
View abstract ⏷
This paper presents a finite control set model predictive control (FCS-MPC) approach to control bi-directional dc-dc converter for battery charger application. The dc bus voltage is controlled by estimating the inductor current reference in boost mode of bi-directional dc-dc converter using the input voltage, output voltage, and output power. The battery is charged by constant current (CC) and constant voltage (CV) control methods. The main control objectives are: 1) regulation of the dc bus voltage at a reference value by supplying the power to the dc bus from the battery, 2) discharging the battery using current control, and 3) charge the battery with CC and CV from the dc bus. This control algorithm is verified via MATLAB/simulink.
Partial Startup Scheme for Smart Transformer in Meshed Hybrid Islanded Grid Operation
Article, IEEE Transactions on Industry Applications, 2022, DOI Link
View abstract ⏷
Smart transformer (ST)-based low-voltage (LV) meshed hybrid grids provide various power flow paths and ensure continuous power supply to loads. The meshed hybrid microgrid can continue supplying to LV loads even during islanding operation. In such a case, the ST LV converter is operational while its medium voltage (MV) converter as well as the isolated dc-dc converter are shut down. This article proposes a step-by-step startup method for these two converters of the ST to establish reconnection of the meshed hybrid LV microgrid to the MVac grid while keeping the ST LV converter functional. The proposed method involves charging the MVdc bus to 85% of the nominal value from the LVdc bus, which is already energized. Next, the ST MV converter is energized to build the MVdc voltage to the final value. Once it is established, the power flow is started, and the transition from islanded to grid-connected mode of the meshed hybrid microgrid is established. To realize the entire starting process, a centralized controller is proposed. This controller gives the on/off commands to the various converters and circuit breakers in the system as per the proposed partial startup algorithm. Stability studies of the ST isolated dc-dc converter are carried out to ensure that the system maintains stability during the starting process. Simulation studies and experimental validation have been performed to verify the proposed starting scheme.
MPC-Based Coordinated Voltage Control in Active Distribution Networks Incorporating CVR and DR
Dutta A., Ganguly S., Kumar C.
Article, IEEE Transactions on Industry Applications, 2022, DOI Link
View abstract ⏷
With massive integration of solar photovoltaics (PVs) in the distribution networks, the voltage regulation problem has become one of the serious concerns for distribution network operators. This article proposes a model predictive-based voltage control that optimally coordinates the reference voltage of distribution static synchronous compensator and on-load tap changer, and PV inverters' active and reactive power set points to maintain network voltages within the operating limits. The two functionalities of the active distribution management system are demand response (DR) and conservation voltage reduction (CVR), which are further explored in the voltage control methodology to enhance energy efficiency of the distribution networks. The proposed methodology is implemented in a 33-bus distribution network to verify its effectiveness for different cases. Furthermore, simulation results demonstrate the benefits of CVR and DR on the proposed methodology.
Multi-Terminal Smart Transformer for Green Data Centres
Das D., Anandh N., Kumar C.
Conference paper, 2022 IEEE 13th International Symposium on Power Electronics for Distributed Generation Systems, PEDG 2022, 2022, DOI Link
View abstract ⏷
With the increasing digitalization in recent times, cloud servers and data centres have gained significant attention. Renewable energy sources (RES) and battery energy storage systems (BESS) are inherent components of green data centres. This has led to an increasing need to develop efficient power electronic solutions. In this paper, a multi-terminal smart transformer (MTST) is proposed for green data centre applications. The proposed system has the capacity to provide quality power both in the form of ac and dc at various required voltage levels. Moreover, the ac and dc terminals also offer the possibility of connecting alternative power sources such as RES or BESS. With such multiple features, the MTST is suggested as a one stop solution for efficient and green power delivery to data centres. All the power requirements of the data centre are provided by the MTST. Thus, there is a reduction in the number of power conversion stages which leads to lower losses. Simulation results are incorporated which verify the operation of the proposed MTST.
Optimal Power Management of Multi-Port Converter System in Electric Vehicle Charging Station
Meikap S., Kumar C., Kumar A.
Conference paper, 2022 IEEE 13th International Symposium on Power Electronics for Distributed Generation Systems, PEDG 2022, 2022, DOI Link
View abstract ⏷
With rising energy storage capacity and distributed generation in the electric grid, optimal power management of converters help to reduce running price and optimize power transfer. This paper develops a particle swarm optimization (PSO) based technique to minimize the cost of energy (CoE) purchased from the grid to reduce the running cost of a multi-port converter system for electric vehicle (EV) charging station. The multi-port system discussed in the paper integrates a photovoltaic (PV) system, battery storage, electric grid, and EV charging system. The developed optimal power management system supervises the controllers of different converters in the multi-port converter system. The performance of the optimal power management system is validated through simulation.
UPS Operation of Multi-Terminal Smart Transformer for Islanded Operation of Data Centres
Das D., Anandh N., Kumar C.
Conference paper, 10th IEEE International Conference on Power Electronics, Drives and Energy Systems, PEDES 2022, 2022, DOI Link
View abstract ⏷
With the ever-growing demand of internet-based services globally, the power demand and energy consumption in data centres are consistently rising. To enhance the efficiency of the power conversion stages from the medium voltage (MV) utility grid to the low voltage (LV) level in data centres, smart transformer (ST) provides a prominent solution. Thereby, significantly decreasing the number of cascaded power conversion stages, ensuing lesser complexity, high reliability, high power density/efficiency of data centre power supplies. In this paper, a multi-terminal (MT) ST is proposed for data centres, and particularly its uninterrupted power supply (UPS) mode of operation for continuity of power supply is explored. The MTST is an extension of the ST by replacing the dual-active bridge in the isolation stage with a multi-active bridge. This allows the ST to have multiple LVdc ports which are utilized for server loads in the data centres and also to exchange power from renewable sources/energy storage systems. The MTST can also be operated as an UPS at times of power outages. The simulation of the proposed system is done in PSCAD software to verify its operation in UPS mode, ensuring uninterrupted power to the data centres.
Model Predictive based Coordinated Voltage Control of Active Distribution Networks with Distributed Generation and Electric Vehicles
Dutta A., Ganguly S., Kumar C.
Conference paper, 4th International Conference on Energy, Power, and Environment, ICEPE 2022, 2022, DOI Link
View abstract ⏷
With increasing integration of electric vehicles (EV) in the distribution network, new challenges have emerged for the power system operators. One of the typical challenges is EV charging coordination for fulfilling EV customers' demands while satisfying storage constraints. This paper presents a model predictive based control (MPC) approach for coordination of different voltage regulation devices and EV charging with the consideration of EV users' stochastic behavior. The proposed approach aims at maintaining the voltages within desired limits as well as charging the EVs according to the charging requests. Simulation results demonstrate that the performance of the proposed coordinated charging is better than the uncontrolled charging.
Single Phase Modular Multilevel Converter for Photovoltaic Application
Gauttam G., Hrishikesan M.V., Kumar C.
Conference paper, 4th International Conference on Energy, Power, and Environment, ICEPE 2022, 2022, DOI Link
View abstract ⏷
This paper presents a control technique for a singlephase modular multilevel converter (MMC) with photovoltaics (PV) integration and having a grid connection. For a PV connected to the grid, MMC is an interfacing unit that acts as a DC to AC converter. This paper proposes a method to solve the problem of controlling the output of the single-phase MMC by designing a controller to get the desired output power. Simulation of the proposed controller with PV integrated system has been performed on MATLAB/Simulink. The simulation results suggest that the proposed control method is a feasible solution to control MMC output in PV integrated grid-connected MMC system.
Smart Transformer Enabled Triple-Active Bridge Converter for Modern Data Centres
Anandh N., Das D., Kumar C.
Conference paper, 2022 22nd National Power Systems Conference, NPSC 2022, 2022, DOI Link
View abstract ⏷
An ever-growing demand of information technology (IT) services, cloud servers and digitalization has led to an exponential increase in the demand for digital storage, power demand, and energy consumption in data centres. In this paper, a smart transformer (ST) enabled triple-Active bridge (TAB) converter for modern data centres is proposed. The smart transformer delivers power from medium voltage (MV) utility grid to low voltage (LV) ac load. The triple-Active bridge (TAB) converter plays a pivotal role in supplying power from LVdc bus down to various low-level dc voltages required by the data centres. This ST enabled TAB converter offers several features such as reduced conversion stages, high frequency power conversion, connection of alternate power sources, higher efficiency, power density and reliability. The proposed system provides both ac and dc powers required by the data centre loads, and this can also be operated in UPS mode to ensure the continuity of power supply. The simulation is done in PSCAD/EMTDC software and the operation of the proposed system is verified.
Power Loss Minimization in Smart Transformer Enabled Low Voltage Islanded Meshed Hybrid Microgrid
Das D., Manojkumar R., Kumar C., Ganguly S.
Article, IEEE Access, 2022, DOI Link
View abstract ⏷
The smart transformer (ST) offers several features in a hybrid microgrid due to the presence of both ac and dc links while providing various power flow paths. For ST based meshed microgrid, continuous operation is highly important and one of the effective ways to achieve it is by minimizing line losses. This paper proposes a power loss minimization strategy which is specific for an ST based islanded meshed hybrid microgrid. In such an islanded system, a battery energy storage system (BESS) is used for maintaining the low voltage (LV) dc bus voltage of ST. The hybrid microgrid consists of renewable energy sources, electric vehicles (EV) charging stations, storage, etc. The minimization of total distribution line power loss is chosen as an objective function for optimization problem. The active power references of distributed generation converters and charge or discharge schedules of EVs are optimally controlled using genetic algorithm while satisfying the various constraints of the system. Further, a smart LV load shedding is also incorporated to the power management. This is activated on crossing the lower critical state of charge of the BESS. It is used as a final measure to increase BESS discharge time resulting in prolonged operation of the islanded system. Simulation and experimental results verify the performance of the proposed scheme. For the various cases considered, the proposed system is compared with conventional power management strategies. It was observed that while in a particular case, the conventional method incurred 1.337 kW losses, the proposed method was able to reduce the line losses to 1.0487 kW. This shows a 22% reduction in line losses with proposed method as compared to conventional method.
A Multi-Port Converter System for Grid Tied Electric Vehicle Charging Station
Meikap S., Das D., Kumar C., Buticchi G.
Conference paper, 2022 IEEE 13th International Symposium on Power Electronics for Distributed Generation Systems, PEDG 2022, 2022, DOI Link
View abstract ⏷
This paper develops a multi-port isolated converter system designed for electric vehicle (EV) charging with an integrated solar photovoltaic (PV) system, battery storage system, and electric grid. For the integration and control of different power sources, a power management system is developed as centralized controller to select sources that will supply power at any instant, depending on load and grid conditions. The power management strategy provides suitable references to controllers of different power converters in multi-port converter for smooth operation. The controller design of different converters for closed loop operation is also developed in this paper. The simulation result validates the operation of the multi-port converter system developed for EV charging application.
Modelling and Control of Modular Multilevel Converter and Dual Active Bridge Based Fast Electric Vehicle Charger
Verma A., Mayank K., Meikap S., Kumar C.
Conference paper, 4th International Conference on Energy, Power, and Environment, ICEPE 2022, 2022, DOI Link
View abstract ⏷
This paper presents modelling and control of medium voltage (MV) grid connected modular multi-level converter (MMC) and dual active bridge (DAB) based isolated electrical vehicle charger. The presented model consists of a half bridge sub module (SM) based MMC as first stage and a DAB as second stage of the charger. Firstly, the equivalent model of MMC and DAB is introduced and then a proper control system is designed for both the converters. For MMC level shifted pulse width modulation (PWM) along with shorting algorithm based capacitor voltage balancing technique is used. Two separate voltage and current control loops are designed for DAB. Charging of battery is carried out in constant current (CC) mode upto 80% of its state of charge (SoC) and in constant voltage (CV) mode after 80% SoC of battery. A proper switching mechanism is introduced to minimise the transients during switch-over of DAB controllers. A 3.3 kV, 200 kVA grid connected MMC with a DAB and a 200 Ah, 700 V Li-ion battery system is simulated. Simulation results in steady state and also during controller switch-over process is presented to verify the charging system.
Modular Multilevel DC-DC Converter Based EV Battery Charger
Prasoon S., Gaurav S., Kumar D., Kumar C.
Conference paper, 10th IEEE International Conference on Power Electronics, Drives and Energy Systems, PEDES 2022, 2022, DOI Link
View abstract ⏷
In the recent times, modular multilevel converter (MMC) is a prominent choice of power electronic converter in medium voltage (MV)/high voltage (HV) applications. The main features of MMC are modular design, scalability, reliability, fault tolerance capability, high step-up ratio and less filtering requirements. This paper presents a transformer-less MMC based electric vehicle (EV) battery charger. A high step-up/down ratio MMC dc-dc converter is designed such that the high input voltage is converted to the battery voltage level. This configuration ensures significant reduction in the complexity of design, system costs and space requirements for fast charging. Phase-shifted pulse width modulation is used to control the MMC operation. The closed-loop operation of the converter is realized using proportional integral (PI) controller for charging of battery in constant current mode till 80% state of charge (SoC) of battery. Further, it is charged in constant voltage mode. A lower arm sub-module (SM) ensures the balanced capacitor voltage without requirement of any additional control architecture. The results are verified using simulation carried out in MATLAB/Simulink environment.
Exploration of Parametric Effect on Fiber Laser Weldments of SS-316L by Response Surface Method
Article, Journal of Materials Engineering and Performance, 2021, DOI Link
View abstract ⏷
Fiber laser welding experiments are conducted on SS316L austenitic stainless steel plates based on the statistical design of experiments technique. A special kind of fixture is designed and fabricated with a facility to provide argon gas and is made up for bead protection. The influence of beam power, welding speed, and defocused position on fusion zone width, fusion zone area, and tensile strength of weldments is studied and discussed briefly. The most influencing factors and their percentage contribution on output responses are identified by analysis of variance technique. Beam power directly influences the bead features, whereas welding speed inversely affects it. However, the defocused position shows an insignificant effect on the fusion zone area within the selected range. The tensile strength increases with an increase in both beam power and welding speed up to a particular optimum value, and beyond that, it starts reducing. The highest hardness value is observed in the fusion zone at ‘1’ mm defocused position below the workpiece surface due to a decrease in grain size and interdendritic spacing. Ductile mode of fracture failure is found in both base material and weldment. The optimum welding condition obtained in this study yields full penetration, narrower weld width, lesser fusion zone area, minimal weld defects, and acceptable tensile strength of weldments.
Recovery of carbon rich material:-Recycling of spent pot lining: A review
Agrawal A., Kumar C., Meshram A.
Conference paper, Materials Today: Proceedings, 2021, DOI Link
View abstract ⏷
Spent pot lining (SPL) is a carbon rich material generated during primary aluminium smelting process. The major constituents of SPL are carbon (40-50%), fluoride (10-18%), aluminium (10-13%), cyanide (700-4500ppm) and sodium (12-16%) along with other metals like calcium, iron, lithium, titanium and magnesium in trace amounts. SPL ends up getting landfilled but the hazardous composition of the waste (presence of fluoride and cyanide), coupled with toxicity and reactivity with water, harm the environment. Gases like methane, ammonia and hydrogen cyanide evolve when SPL is exposed to water. Water and soil resources are hampered due to the SPL landfilling. This review focuses on the recovery of carbon and fluoride for its utilization as fuel in cement industry and as a carbonaceous material in iron making industry. The article describes hydrometallurgical extraction processes from different grades of SPL in which cyanide is extracted in water washing stage whereas fluoride is recovered as CaF2. The acid leaching (by sulphuric acid, perchloric acid, hydrofluoric acid and hydrofluorosilicic acid) removes the rest of the fluorides, silicates, cryolite, alumina and aluminium fluoride. Final treated SPL is used as reducing agent in iron making industry. SPL has high mechanical strength against breakage, abrasion and compression. Due to these features it can be used as granulated material in reduction reactors. This review article discusses the composition of different grades of SPL, the environmental impacts, methods for recovery of carbon, corundum, cyanides and fluorides and its applications in iron making and cement industry in economical and environment friendly manner.
Fiber laser welding of Ti-6Al-4V alloy
Kumar C., Paul C.P., Das M., Bindra K.S.
Book chapter, Advanced Welding and Deforming, 2021, DOI Link
View abstract ⏷
In the present chapter, the fundamentals of laser beam welding technologies are discussed in detail. The basic principle of laser generation, behavior, and characteristics of a laser beam are elucidated. The working principles of fiber laser, their construction, and advantages over other lasers are explored. Also, various welding process parameters which affect the quality of weldments are discussed. The titanium alloys possess an outstanding combination of lightweight, moderate corrosion resistance, and high specific strength. However, it becomes highly reactive beyond 300°C temperature. Therefore, the weldability aspects of Ti-6Al-4V are also discussed. The need for the design and fabrication of a shielding gas delivery system in laser welding of Ti-6Al-4V alloy is explored. The mechanism of phase transformation in the fusion zone is discussed briefly. The dependencies of various kinds of weld bead features on process parameters, a microstructural study in fusion and heat-affected zones, mechanical properties such as hardness, tensile properties, and different types of weld bead defects are discussed. The modes of fracture failure during tensile testing of fiber laser weldments of Ti-6Al-4V material are discussed. Also, it explores the prospects of the development of laser welding set-up in the future by considering their cost, beam quality, portability, and robust design.
Optimal Peak Shaving Control Using Dynamic Demand and Feed-In Limits for Grid-Connected PV Sources with Batteries
Manojkumar R., Kumar C., Ganguly S., Catalao J.P.S.
Article, IEEE Systems Journal, 2021, DOI Link
View abstract ⏷
Peak shaving of utility grid power is an important application, which benefits both grid operators and end users. In this article, an optimal rule-based peak shaving control strategy with dynamic demand and feed-in limits is proposed for grid-connected photovoltaic (PV) systems with battery energy storage systems. A method to determine demand and feed-in limits depending on the day-ahead predictions of load demand and PV power profiles is developed. Furthermore, an optimal rule-based control strategy that determines day-ahead charge/discharge schedules of battery for peak shaving of utility grid power is proposed. The rules are formulated such that the peak utility grid demand and feed-in powers are limited to the corresponding demand and feed-in limits of the day, respectively, while ensuring that the state-of-charge (SoC) of the battery at the end of the day is the same as the SoC of the start of the day. The optimal inputs required for applying the proposed rule-based control strategy are determined using a genetic algorithm for minimizing peak energy drawn from the utility grid. The proposed control algorithm is tested for various PV power and load demand profiles using MATLAB.
Increasing Voltage Support Using Smart Power Converter Based Energy Storage System and Load Control
Hrishikesan V.M., Das D., Kumar C., Gooi H.B., Mekhilef S., Guo X.
Article, IEEE Transactions on Industrial Electronics, 2021, DOI Link
View abstract ⏷
Voltage sag and swell affect the normal operation of loads as well as distributed generating sources and reduce the overall reliability of the system. For improving the voltage at point of common coupling, different grid code requires control of active and reactive powers through power electronic solutions. In this article, a smart power converter (SPC) is introduced in the distribution grid, and different from the existing voltage support solutions, this article utilizes control and coordination capabilities of SPC to provide medium voltage (MV) grid voltage support during voltage sag/swell. The proposed control scheme aims to improve the voltage support capability of SPC in the MV grid by the coordinated operation of SPC MV converter, low voltage converter, and battery energy storage system (BESS). For achieving the same voltage support capability, the proposed method requires lower rated BESS as compared to existing solutions. Simulation and experimental results show the effectiveness of the proposed scheme.
Coordinated Voltage Control of Active Distribution Networks in presence of PV and Energy Storage System
Dutta A., Ganguly S., Kumar C.
Conference paper, Proceedings of the Energy Conversion Congress and Exposition - Asia, ECCE Asia 2021, 2021, DOI Link
View abstract ⏷
This paper proposes a rule-based model predictive control (MPC) approach to coordinate the operation of distributed generation units (DGU), energy storage systems (ESS), and on-load tap changer (OLTC). The control approach manages the settings of the regulating devices optimally in order to regulate node voltages and minimizes power loss effectively with the aid of minimal control resources. Three rules are devised for MPC on the basis of magnitudes of voltages. The objectives for MPC are changed according to these pre-defined rules. The effectiveness of the proposed approach is tested in a 33-bus distribution network. It has been found that the proposed control scheme could mitigate voltage violations as well as energy loss in both normal and abnormal conditions. Moreover, the performance of the proposed control scheme with ESS is better than without ESS in terms of less usage of control resources, and reduced energy losses. Simulations are also carried out to test the robustness of the control scheme. The performance of the proposed control scheme is further investigated with distributed ESS.
Optimal Placement of Smart Transformer Low Voltage Converter in Meshed Hybrid Distribution Network
Kumar C., Manojkumar R., Ganguly S.
Conference paper, Proceedings of the Energy Conversion Congress and Exposition - Asia, ECCE Asia 2021, 2021, DOI Link
View abstract ⏷
Smart Transformer (ST) is an effective solution for improving the performance of electric grid with significant renewable energy integration. This paper proposes a methodology for optimal placement of ST low voltage (LV) converter in meshed hybrid distribution network. The ST LV converter is placed at the different buses to find out its optimal location, while ensuring that the energy drawn from the grid is minimized and line voltages are maintained within the grid codes. Moreover, a method of determining power flow solution is proposed to generate the active and reactive power references for distributed generation converters. The proposed work is tested on the considered system for various locations of ST LV converter using MATLAB simulations.
Optimal Power Management for Islanded Operation of ST-based Meshed Hybrid LV Microgrid
Das D., Manojkumar R., Kumar C., Ganguly S.
Conference paper, Proceedings of the Energy Conversion Congress and Exposition - Asia, ECCE Asia 2021, 2021, DOI Link
View abstract ⏷
This paper proposes an optimal power management strategy for the islanded operation of smart transformer (ST)-based meshed hybrid low voltage (LV) microgrid. The main objective is to ensure that the line losses in the system are minimum. Accordingly, the power management scheme decides the reference powers for the storage systems and distributed generation (DG) converters during islanded operation. This ensures that the system has the maximum possible operation time with the available DG sources, battery energy storage systems and electric vehicles (EV). In case of surplus power generation, EVs are utilized for storage. This ensures that minimum DG power has to be curtailed, leading to maximum utilization of DG resources. The optimal power management problem is solved using genetic algorithm in MATLAB. Further, the proposed optimal power management strategy is verified through PSCAD simulations on the considered system of islanded ST based meshed hybrid LV grid.
Single-Phase Step-Up Switched-Capacitor-Based Multilevel Inverter Topology with SHEPWM
Siddique M.D., Mekhilef S., Padmanaban S., Memon M.A., Kumar C.
Article, IEEE Transactions on Industry Applications, 2021, DOI Link
View abstract ⏷
Multilevel inverter (MLI) topologies play a crucial role in the dc-ac power conversion due to their high-quality performance and efficiency. This article aims to propose a new switched-capacitor-based boost multilevel inverter topology (SCMLI). The proposed topology consists of nine power semiconductor switches with one dc voltage source and two capacitors, capable of generating a nine-level output voltage waveform with twice voltage gain. With the addition of two switches, the proposed topology can be used for higher voltage-gain applications. Other features of the proposed topology include the self-voltage balancing of the capacitors, parallel operation of the capacitors, lower voltage stress across the switches, along with the inherent polarity changing capability. To obtain the high-quality output waveform, a selective harmonic elimination pulsewidth modulation technique is applied. In this technique, the detrimental low-order harmonics can easily be regulated and eliminated from the output voltage of MLI. The proposed topology is compared with the recently introduced SCMLI topologies considering various parameters to set the benchmark of the proposed topology. The performance of the proposed MLI is investigated through various experimental results using a laboratory prototype setup.
Operation and Control of the Smart Transformer in Meshed and Hybrid Grids: Choosing the Appropriate Smart Transformer Control and Operation Scheme
Zhu R., Liserre M., Langwasser M., Kumar C.
Article, IEEE Industrial Electronics Magazine, 2021, DOI Link
View abstract ⏷
The impact of low-carbon technologies, like renewable energies and electric vehicle (EV) charging stations, will be an additional strain in terms of voltage violation and current congestion on the low-voltage network, resulting in a reduced quality of supply and overheating assets. To avoid or defer the replacement of these traditional assets, the network of the future needs an intelligent solution such as smart transformers (STs) [1]. The ST is a solid-state transformer with smart control functionalities as proposed in [2].
Operation of Meshed Hybrid Microgrid during Adverse Grid Conditions with Storage Integrated Smart Transformer
Article, IEEE Open Journal of the Industrial Electronics Society, 2021, DOI Link
View abstract ⏷
Microgrid faces various challenges such as reverse power flow, peak power demand, voltage limit violations, etc., due to significant installations of renewable energy sources (RESs) and electric vehicles (EVs). For continuous and effective operation of such a system, enhanced and complex control methodologies are needed. Smart transformer (ST) has emerged as a promising solution for overcoming such challenging issues. This paper proposes the operation of battery energy storage system (BESS) integrated ST in a meshed hybrid microgrid. Instead of connecting through ac interconnections with normally open (NO) circuit breakers (CBs), the same line is connected through the medium voltage (MV) dc links of ST. This introduces several paths for controlled power flow in the system. As compared to ac interconnections, this configuration improves the performance of the overall system during various adverse operating conditions such as reverse power flow, peak power demand, and voltage sag. Moreover, the MVDC line voltage is controlled by one ST, resulting in reduced control complexity of other power converters. Detailed simulation and experimental results are provided to show the merits of the proposed system.
Smart Transformer as a Variable Frequency Transformer
Conference paper, 2021 6th IEEE Workshop on the Electronic Grid, eGRID 2021, 2021, DOI Link
View abstract ⏷
A variable frequency transformer (VFT) is a power transfer device used to exchange power between two grids operating at different frequencies. Conventional VFTs are rotational machines working on the principle of induction. This paper proposes the use of a smart transformer (ST) as a VFT. Conventional VFTs have issues like uncontrolled reactive power flow, high power torque fluctuations, etc. These issues can be mitigated by using ST as a VFT. To handle power levels at which VFTs generally work, design procedures for the ST converters are explained. Such a connection of asynchronous grids with ST is also advantageous over conventional HVdc solutions. The line frequency transformers used in HVdc systems are replaced, and high frequency transformer used in ST helps reduce the size and weight of the system. Moreover, additional dc links of the ST allow for connection to MVdc grids, renewable energy systems, storage, etc. Simulation results show satisfactory operation of the proposed scheme.
Dynamic Voltage Control Using Unified Power Quality Conditioner with Storage
Hrishikesan V.M., Kumar D., Kumar C.
Conference paper, 2021 IEEE 15th International Conference on Compatibility, Power Electronics and Power Engineering, CPE-POWERENG 2021, 2021, DOI Link
View abstract ⏷
The growth of distributed generation (DG) and electric vehicles (EVs) in the distribution grid demand improved control of active and reactive powers. The enhanced control helps in maintaining the voltage variations within the grid-code specified limits. A unified power quality conditioner (UPQC) protects the loads and DG from grid voltage disturbances. However, the series converter of UPQC remains underutilized because it is only utilized during grid voltage violations. This paper proposes a dynamic voltage control using UPQC, which helps in (1) improving the utilization of the UPQC series converter, (2) maintaining a grid-code specified voltage profile throughout the distribution grid during extreme load and generation conditions. Simulation results are provided in the paper to show the effectiveness of the proposed control strategy.
Smart Transformer-Enabled Meshed Hybrid Distribution Grid
Das D., Hrishikesan V.M., Kumar C., Liserre M.
Article, IEEE Transactions on Industrial Electronics, 2021, DOI Link
View abstract ⏷
Renewable energy sources (RES) induce problems such as voltage and current limit violations, absence of inertia and consequent stability problems, and poor power quality. Smart transformer (ST) is a promising solution for avoiding such a changing grid scenario leading to strong grid reinforcements. This article proposes an ST-enabled meshed hybrid distribution grid to achieve voltage and power flow control simultaneously with a centralized controller. In this configuration, a low-voltage dc (LVdc) line is proposed which connects the ST LVdc link with the dc bus of distributed generation (DG) converters. This introduces various active power flow paths to support the loads. The DG converters supply active power near the load points which ensures that line losses are reduced significantly while achieving improved voltage regulation as compared to conventional microgrid. Moreover, the DG converters can draw active power from ST LVdc link during absence of RES to support the load, resulting in improved utilization of these converters. The control complexity of the DG converters is reduced as the ST controls both the LVac and LVdc line voltages. Further, the newly developed power flow path allows reverse power flow from DG plants more efficiently. Performance of the proposed system is verified with simulation and experimental results.
Operation and Control of Unified Power Quality Conditioner Enabled Meshed Hybrid Microgrid
Hrishikesan V.M., Kumar D., Das D., Kumar C.
Conference paper, 2021 IEEE 15th International Conference on Compatibility, Power Electronics and Power Engineering, CPE-POWERENG 2021, 2021, DOI Link
View abstract ⏷
In a distribution system with a larger number of renewable energy sources, improved power control measures are required to maintain the voltage and current quality within the grid-code specified limits. The unified power quality conditioner (UPQC) is a promising option in this scenario that can control the AC load voltages and source currents. This paper proposes a UPQC based meshed hybrid microgrid configuration where the DC bus of the UPQC is extended to form an LVDC line. Different loads and sources are integrated into the DC line. Various power flow conditions are analyzed, which show the power management features of the proposed system. In addition, the grid voltage sag condition is also analyzed, and improved performance is observed.
Impact of Optimal Control of Distributed Generation Converters in Smart Transformer Based Meshed Hybrid Distribution Network
Kumar C., Manojkumar R., Ganguly S., Liserre M.
Article, IEEE Access, 2021, DOI Link
View abstract ⏷
A smart transformer (ST) based meshed hybrid distribution network is realized by extending ST low voltage dc (LVDC) link to form a LVDC line which connects dc buses of existing distributed generation (DG) converters. This paper proposes a method for optimal operation in such ST based meshed hybrid distribution network. A CIGRE LV residential distribution network with DG sources is connected at ST low voltage ac (LVAC) and LVDC terminals. All the DG sources are connected to LVDC line. The power management scheme and method of determining power flow solution for the considered distribution network are proposed. An optimal problem is formulated for determining the active and reactive power references of DG converters while maintaining the LVAC load bus voltages within the grid limits and considering the DG converters constraints. The minimization of energy drawn from ST medium voltage (STMV) grid is considered as objective function and solved using genetic algorithm. To know the impact of proposed optimal control of DG converters, various performance indicators i.e., energy loss, operating energy costs, voltage profile and sizing of ST converters are considered and compared with existing literature.
The Role of Renewable Energy System in Reshaping the Electrical Grid Scenario
Buticchi G., Lam C.-S., Ruan X., Liserre M., Barater D., Benbouzid M., Gomis-Bellmunt O., Paja C., Kumar C., Zhu R.
Article, IEEE Open Journal of the Industrial Electronics Society, 2021, DOI Link
View abstract ⏷
Renewable Energy Systems have been in the spotlight of the academic and industrial research for more than two decades, thanks to the development of several fields related to the Electrical Engineering. More recently, with the increasing complexity of the individual renewable energy systems and the interconnection to the grid, the scientific panorama has been witnessing to a convergence of different topics, which span across several IEEE-IES thematic areas: power electronics, electrical machines, smart grids, energy storage, transportation electrification and aerospace. After a brief overview of the renewable energy technologies, this work deals with how the convergence of multiple technologies developed to provide marginal support to the grid has evolved into the foundation of the future utility grid and expanded to transportation sector. It will be shown how the design of a renewable energy system cannot prescind anymore from the electrical grid and from the ancillary services that are requested. Example of convergence are given for a smart transformer application and for a transportation application.
Microstructural Characterization of Ti-6Al-4V Alloy Fiber Laser Weldments
Conference paper, Lecture Notes in Mechanical Engineering, 2020, DOI Link
View abstract ⏷
The quality of fiber laser welded specimens of Ti-6Al-4V alloy plates in butt joint is examined. A special kind of fixture is designed and fabricated for providing shielding gas. The microstructural analysis at various positions within heat-affected zone and in fusion zone are explored and its microstructural morphologies are compared. Due to the chronological distribution of temperature gradient, a nonhomogeneous microstructure is developed from fusion zone to base metal zone. Various kinds of microstructural morphology of martensitic structure, i.e., α′ martensite, massive α (αm), and blocky α are found in fusion zone. Also, the variations in amount of α′ martensite are found inside heat-affected zones. Maximum hardness is obtained in fusion zone due to the occurrence of higher quantity of α′ martensitic structure.
Improved power sharing and voltage regulation with modified droop control in microgrid
Conference paper, 2020 21st National Power Systems Conference, NPSC 2020, 2020, DOI Link
View abstract ⏷
Power sharing and load voltage regulation requires the knowledge of feeder impedance which is one of the biggest demerit of conventional droop control. This paper proposes a new method to overcome this demerit by the use of numerical approach and a new voltage regulation technique. Modified angle droop and voltage droop is proposed for intended sharing ratio and transfer of active and reactive powers. The proposed method can work with different type of feeder impedance using a single droop law. Accurate sharing of active and reactive power while maintaining constant load voltage without the knowledge of feeder impedance is the main contribution of this paper. Simulation results are shown to verify the proposed scheme.
Optimal demand response using dynamic electricity price limit in a hybrid AC/DC system
Manojkumar R., Kumar C., Ganguly S.
Conference paper, 2020 21st National Power Systems Conference, NPSC 2020, 2020, DOI Link
View abstract ⏷
Demand response (DR) is an important characteristic of a smart grid that benefits both power system operators and electricity consumers. In this paper, an optimal DR with a dynamic electricity price limit is proposed for a grid-connected ac/dc hybrid microgrid. The considered system consists of ac/dc loads, photovoltaic source, and battery energy storage system. The electricity price limit is determined using day-ahead pricing of electricity, predictions of ac/dc load, and PV power profiles. An optimal rule-based DR control algorithm that determines day-ahead charge/discharge schedules of battery for minimizing the energy costs of the system is developed. The rules are formulated such that there is no power drawn from the grid when the electricity price is more than the electricity price limit while ensuring that the state of charge (SoC) of battery at the end of the day is same as SoC of the start of the day. The optimal inputs required for applying proposed DR are determined using genetic algorithm in MATLAB.
Partial Start-up Scheme for ST to Reconnect to MV Grid from LV Side Islanded Operation
Conference paper, 9th IEEE International Conference on Power Electronics, Drives and Energy Systems, PEDES 2020, 2020, DOI Link
View abstract ⏷
This paper proposes a partial start-up procedure for a smart transformer (ST) to changeover from low voltage (LV) side islanded operation to grid connected mode. In the islanded operation of ST LV side, the ST LV converter is operational but the other two converters of the ST namely the ST medium voltage (MV) converter and ST isolated dc-dc converter are shut down. For the reconnection to the MV grid, these converters have to be switched on to enable power flow. Thus while one portion of the ST is already operational, the non-operational parts have to be started without affecting or interrupting the operation of the LV grid. This calls for a proper stage by stage start-up procedure to ensure that the converters become operational maintaining the staring inrush currents within rated limits of the converters. A reverse start up scheme is proposed where the ST MVdc bus is charged by drawing power from the battery energy storage system connected to the LVdc bus. Subsequently the ST MV converter is started to connect the LV side to the MV grid. Simulation results are incorporated which verify the proposed start-up scheme.
Model predictive control based coordinated voltage control in active distribution networks utilizing OLTC and dstatcom
Dutta A., Ganguly S., Kumar C.
Conference paper, 9th IEEE International Conference on Power Electronics, Drives and Energy Systems, PEDES 2020, 2020, DOI Link
View abstract ⏷
The rapid growth of solar photovoltaics (PV) has brought tremendous challenges to the distribution network operators. Voltage regulation is one of the serious concerns in the renewables-interfaced distribution networks. This paper proposes a control strategy to coordinate distribution static synchronous compensator (DSTATCOM) along with active power curtailment and on-load tap changer to ensure acceptable voltage magnitudes across distribution networks. The coordinated control strategy is based on model predictive control (MPC). The effectiveness of the proposed methodology is verified on a 33-bus distribution network. Further, simulations are performed to study the effects of DSTATCOM in voltage regulation and compare the effects of DSTATCOM and PV inverter as reactive power compensation devices in networks. The test system is further simulated with a sudden large voltage increase in the slack bus of the network. Active power curtailment is considered as the emergency control action for all the scenarios.
Multifunctional model predictive control of grid connected voltage source converter
Kumar D., Das D., Kumar C.
Conference paper, 9th IEEE International Conference on Power Electronics, Drives and Energy Systems, PEDES 2020, 2020, DOI Link
View abstract ⏷
This paper presents a multifunctional grid connected voltage source converter (VSC), controlled using model predictive control. The VSC acts as an interface between various non-conventional sources and the grid. The DC side of VSC interfaces a solar photovoltaic plant, battery, and supercapacitor systems and an effective power management strategy is developed. The battery is used to either supply or store power and the supercapacitor supplies during power surges or transients. Functional features of the VSC include balancing of grid current, supplying harmonic and reactive components of load current and active power. Simulation results have been shown to validate the functioning of the VSC.
A New Voltage Control Strategy to Improve Performance of DSTATCOM in Electric Grid
Chandan K., Mishra M.K., Mekhilef S.
Article, CES Transactions on Electrical Machines and Systems, 2020, DOI Link
View abstract ⏷
A new voltage control strategy of distribution static compensator (DSTATCOM) has been proposed in this paper for electric grid applications. The proposed control scheme combines two methods of DSTATCOM operation to improve its performance. Considering power factor and voltage magnitude as degree of freedom, the DSTATCOM provides features such as mitigation of voltage and current harmonics, balancing of source currents, improvement of power factor, voltage regulation during voltage sag and swell, reduction in inverter losses, and control of load power to achieve energy conservation. The performance of proposed DSTATCOM control is better as compared to its conventional operation at any time of operation. PSCAD simulation and experimental results validate the performances.
BESS-PV Integrated Islanded Operation of ST-based Meshed Hybrid Microgrid
Das D., V.m. H., Kumar C.
Conference paper, 2020 IEEE 9th International Power Electronics and Motion Control Conference, IPEMC 2020 ECCE Asia, 2020, DOI Link
View abstract ⏷
Smart transformer (ST) has emerged as a promising solution for interfacing energy sources into the electric grid. Due to increase in DC sources and loads in the distribution grid, hybrid grids have gained popularity where there is parallel existence of AC and DC subgrids. This paper proposes a battery energy storage system (BESS) and photovoltaic (PV) integrated three stage ST-based meshed hybrid microgrid. The proposed system operates low voltage (LV) side of microgrid in islanded mode. When islanding is necessary, whether due to faults or maintenance, the mode of operation of the BESS is changed from current controlled mode (CCM) to voltage controlled mode (VCM) to maintain the voltage at the ST LVDC link. This ensures that the LV grid along with all the distributed generation (DG) converters operate undisturbed. A power management strategy for an LV side islanded operation of the distribution grid is proposed. With the control of LVAC voltage, the BESS critical state of charge (SOC) information is communicated to the LVAC side loads for connection or disconnection. Moreover, in the proposed scheme, as the islanding is done at the MVAC grid, the issues of synchronization during re-closure do not arise for all DG converters.
Control and Sizing of Two-Stage Smart Transformer in Meshed Hybrid Distribution Grid
Kumar C., Vm H., Das D., Ghosh S.
Conference paper, 2020 IEEE 9th International Power Electronics and Motion Control Conference, IPEMC 2020 ECCE Asia, 2020, DOI Link
View abstract ⏷
Increased penetration of renewable energy in electric distribution grid requires installation of more power electronics devices and complex controller. In such scenario, smart transformer (ST) is a promising solution as it can control both power and voltage simultaneously with available dc links to integrate batteries and electric vehicles. This paper propose an ST-based meshed hybrid distribution grid where low voltage (LV) ST power converter is eliminated and realized by the distributed generation (DG) converters. The DG converters are connected through the extended LVDC line formed by the ST LVDC link. This configuration significantly reduces the rating of power converters in LV grid. Moreover, the LV side DG converters are operated with droop control which allows power management in LV grid without any communications among the DG converters.
Model predictive control-based optimal voltage regulation of active distribution networks with OLTC and reactive power capability of PV inverters
Dutta A., Ganguly S., Kumar C.
Article, IET Generation, Transmission and Distribution, 2020, DOI Link
View abstract ⏷
This study presents a model predictive control (MPC)-based centralised control approach for maintaining the voltagesof the nodes within permissible limits in the presence of high photovoltaic (PV) penetration. The proposed control schemecoordinates the actions of on-load tap changer (OLTC) and PV inverters optimally to fulfil the desired objectives. The objectivesare minimisation of change in control variables, slack variables, energy loss, and voltage error. These objectives are weighted toform the overall objective function. Three rules are formulated based on the severity of voltage magnitudes. The weights of theobjectives are adjusted according to these pre-defined rules. Simulations are performed in an active distribution network (ADN)integrated with and without microgrids, where both demands and generations vary hourly over the day. As power is injected bythe microgrids during most of the time of the day, the excursions of node voltages are slightly higher in the microgrids integratedADN. Moreover, the incorporation of the proposed rule-based MPC drastically reduces the energy loss due to active power lossin distribution networks, as is evident from the simulation results obtained by comparing the proposed approach with an existingMPC-based approach.
Voltage control using smart transformer via dynamic optimal setpoints and limit tolerance in a residential distribution network with PV sources
Manojkumar R., Kumar C., Ganguly S., Gooi H.B., Mekhilef S.
Article, IET Generation, Transmission and Distribution, 2020, DOI Link
View abstract ⏷
Uncertainities and variations of power generation through photovoltaic (PV) sources are major challenges for theirintegration with the distribution grid. Voltage rise and voltage drop issues limit the increase in PV penetration and loading levels,respectively. Moreover, it is important to maintain voltage levels as per grid code while ensuring that the PV power generation isnot curtailed. In this paper, a voltage control method using smart transformer (ST) via dynamic optimal setpoints and limittolerance is proposed in a residential distribution network. Performance indicators are developed to understand the impact ofthe proposed method on the system voltage profile. A method to determine the optimal inputs for voltage control methodsdepending on the day-ahead predictions of load demand and PV power profiles is developed. Further, a voltage control methodof switching among three setpoints based on the voltage that determines the load side ac reference voltages for ST is proposed.The proposed method is compared with the method of switching between two setpoints based on current. The proposed methodprovides an improved voltage profile in the distribution network, which is tested on a CIGRE low voltage residential distributionnetwork using PSCAD.
Smart Transformer Based Meshed Hybrid Microgrid with MVDC Interconnection
Hrishikesan V.M., Kumar C.
Conference paper, IECON Proceedings (Industrial Electronics Conference), 2020, DOI Link
View abstract ⏷
Efficient power management functions are essential in microgrids with a substantial integration of distributed generation (DG) units to maintain good power quality and reliability for the customers. The microgrid interconnections significantly improve the power management capabilities, and the medium voltage (MV) dc systems are considered to be a promising option for this purpose. The ac-dc interconnections are realized using power electronic solutions. This paper proposes a smart transformer (ST) enabled MVDC interconnected meshed hybrid microgrid. The STs' capability to form the MVDC bus is explored in this paper to establish an MVDC distribution line with a battery energy storage system (BESS) integration. This restructuring introduces multiple paths for the controlled active power flow in the overall microgrid. Moreover, the performance of the system is analyzed during voltage sag, and the operational flexibility of the proposed system is presented through simulation results.
Power Loss Minimization in Smart Transformer Based Meshed Hybrid Distribution Network
Kumar C., Manojkumar R., Ganguly S., Liserre M.
Conference paper, IECON Proceedings (Industrial Electronics Conference), 2020, DOI Link
View abstract ⏷
A smart transformer (ST) based meshed hybrid distribution network is realized by extending ST low voltage dc (LVDC) link to form a LVDC line which connects dc buses of existing distributed generation (DG) converters. This paper proposes a method for power loss minimization in such ST based meshed hybrid distribution network. A CIGRE LV residential distribution network with DG sources is connected at ST LVAC and LVDC terminals. An online optimal problem is formulated for determining the active and reactive power references of DG converters for minimized power losses in line. The total power loss minimization at each time is chosen as the objective function and solved using genetic algorithm. The total loss in the system is the sum of both LVAC and LVDC line losses. This total loss is calculated using the backward forward sweep power flow method. The proposed method is tested in MATLAB.
Capacity Enhancement of a Radial Distribution Grid Using Smart Transformer
Hrishikesan V.M., Deka A.K., Kumar C.
Article, IEEE Access, 2020, DOI Link
View abstract ⏷
Distributed generation (DG) and electric vehicle (EV) are increasingly installed in the modern microgrids (MGs). This demands for an improvement in the power handling capacity of the existing distribution feeders. The power handling capacity of a feeder is limited by the voltage magnitude violation caused by overloading. The smart transformer (ST) is proposed as an effective solution for improving the performance of modern MG. This paper utilizes the power management capabilities of the ST with an integrated battery energy storage system (BESS) for improving the power handling capacity of a medium voltage (MV) 5-bus radial feeder. The proposed method demonstrates the ST's capability to control the active and/or reactive power flow at the MV grid for maintaining the steady-state voltage magnitude within the grid-specified limit. A sensitivity analysis based design study is proposed to determine the power rating requirements for different ST and BESS converters during distinct power control scenarios. The analysis shows the capability of ST in injecting/absorbing active and reactive powers in flexible combinations for achieving the desired voltage magnitudes. The findings are verified through simulation and experimental results.
Weld Quality Assessment in Fiber Laser Weldments of Ti-6Al-4V Alloy
Kumar C., Das M., Paul C.P., Bindra K.S.
Article, Journal of Materials Engineering and Performance, 2019, DOI Link
View abstract ⏷
Laser welding experiments are performed on Ti-6Al-4V alloy sheets by adopting fiber laser. A special kind of workpiece fixture is designed and fabricated for providing shielding gas. After experiments, penetration depth, fusion zone width and heat-affected zone size at different locations within weld bead are measured and discussed in detail. Influence of line energies on the formation of non-uniform microstructure within weld bead is explored by conducting microstructural analysis. Various kinds of microstructural morphology of martensitic structure such as α′ martensite, blocky α, massive α and basket-weave microstructure are found in fusion zone. Experimentally, it is found that beam power is the key parameter for controlling penetration depth. Higher hardness is noticed within fusion zone due to the existence of large volume of α′ martensite. Tensile strength and hardness of welded specimens are increased with decreasing line energy. Small amount of micropores are also found in solidified weld bead. However, its sizes are in acceptable range as per BSEN:4678 standard. Most favorable welding condition is identified as a combination of beam power of 800 W and welding speed of 1000 mm/min which yields full penetration, narrower bead width, small heat-affected zone, minimal defects and acceptable mechanical properties.
Experimental Study of Fiber Laser Weldments of 5 mm Thick Ti–6Al–4V Alloy
Kumar C., Das M., Paul C.P., Singh B.
Book chapter, Lecture Notes on Multidisciplinary Industrial Engineering, 2019, DOI Link
View abstract ⏷
Titanium and its alloys are known as a workhorse for aerospace and automobile industries. These alloys possess several features like high strength, better corrosion resistance, lower density, and very good biocompatibility. It is extensively used in chemical, aviation, aerospace, medicinal, and automotive industries. In this study, an experimental investigation and metallurgical characterization of fiber laser weldments of 5 mm thick Ti–6Al–4V alloy plate are performed. After experiments, the qualities of the welded specimens are investigated in terms of penetration depth, weld appearance, bead geometry, hardness, and developed microstructures in fusion and heat-affected zones. The energy dispersive X-ray spectroscopy analysis confirms shielding gas effectiveness. The microstructures in fusion zone, as well as heat affected zones, are suitably controlled by welding process parameters. The Vickers microhardness of the welded specimens highly depends on developed microstructures in the fusion and heat-affected zones. The results show that the beam power in laser welding process plays a major role for full penetration in the base plate. There is a critical range of welding power that produces full penetration, narrow weld width, small HAZ, and aesthetic bead appearance with satisfactory bead hardening.
Voltage Control in Active Distribution Networks and an Approach based on Model Predictive Control
Dutta A., Ganguly S., Kumar C.
Conference paper, 2019 8th International Conference on Power Systems: Transition towards Sustainable, Smart and Flexible Grids, ICPS 2019, 2019, DOI Link
View abstract ⏷
With the rise in penetration of renewable energy sources in electric distribution networks, reliable operation and control of power system have become a challenge for power system operators. The paradigm shift from passive to active distribution network causes various issues such as, stability, voltage and frequency regulation, designing of protection equipment, etc. Thus, there arises the need of a proper control strategy to deal with such concerns. This paper presents a review of the voltage control strategies already existed in literature. Subsequently, a methodology is also proposed here to regulate voltages in active distribution networks.
Voltage Control Using Smart Transformer for Increasing Photovoltaic Penetration in a Distribution Grid
Manojkumar R., Hrishikesan V.M., Kumar C., Ganguly S.
Conference paper, 2019 20th International Conference on Intelligent System Application to Power Systems, ISAP 2019, 2019, DOI Link
View abstract ⏷
Uncertainty and variation of power generation through photovoltaic (PV) sources are major challenges for their integration with the distribution grid. Voltage rise and voltage drop issues limit the increase in PV penetration and loading level, respectively. It is important to maintain voltage levels within specified limits of grid code for providing long life, more efficiency, and good performance of consumer equipment while ensuring that the PV power generation is not curtailed. In this paper, a voltage control method for the smart transformer (ST) is proposed to improve voltage profile in the distribution network. Voltage control capability for ST is added through the method of switching among three setpoints based on the voltage. The proposed method is compared with the conventional method of switching between two setpoints based on current. The proposed method provides better voltage profile in the distribution network as compared to conventional method. Performance indicators are developed to understand the impact of voltage control methods on the system voltage profile. Proposed voltage control method is tested on a CIGRE low voltage residential distribution network.
A New Single-Phase Single Source Nine Level Boost Inverter Topology
Siddique M.D., Mekhilef S., Shah N.M., Kumar C.
Conference paper, IECON Proceedings (Industrial Electronics Conference), 2019, DOI Link
View abstract ⏷
This paper proposed a new single-phase single stage single source nine-level boost inverter topology with self-voltage balancing along with the reduce switch count. The proposed topology is aimed to design for the renewable energy sources interfacing to the loads, which require higher voltage magnitudes. The proposed topology gives twice voltage booting feature without using any dc-dc converter. The topology proposed in this paper uses a single dc voltage source with two capacitors to generate a nine-level output voltage waveform. Nearest level control modulation technique has been used for the generation of gate pulse for the different switches used in the proposed structure. Different simulation results have been provided using PLECS software, and these simulation results have been verified using the experimental results obtained from a laboratory prototype.
Characteristics of fiber laser weldments of two phases (α+β) titanium alloy
Kumar C., Das M., Paul C.P., Bindra K.S.
Article, Journal of Manufacturing Processes, 2018, DOI Link
View abstract ⏷
Laser welding experiments are conducted at various welding conditions on Ti-6Al-4 V alloy plates by employing fiber laser. A special type of workpiece fixture having provision of supplying shielding gas is fabricated for the protection of weld bead efficiently from environmental contamination. The influence of process parameters i.e. welding speed on the development of non-homogeneous microstructure of the weld bead is investigated by conducting microstructural characterization in details. Different morphologies of martensitic phase such as α´martensite, massive αm, blocky α and basket-weave structure are observed in the fusion zone. The variation in amount of α´ martensite is observed within heat affected zone. The calculated cooling rate and microstructure evaluation in the fusion zone are consistent with the continuous cooling transformation curve of Ti-6Al-4 V alloy. Higher hardness is found in fusion zone of the weldments. At lower welding speeds (500 ̶ 600 mm/min), underfill weld defects and at higher welding speed (800 mm/min) the micro-pores are observed in the weld bead. However, sizes of micro-pores are within the acceptable range as per BSEN: 4678 European standard. The microhardness and tensile strength of weldments are increased with increasing welding speed due to the development of finer α´ martensite in the fusion zone. For a fixed beam power of 1200 W, the most favorable range of welding speed (700 ̶ 800 mm/min) is identified which produced consistently high quality welds without crack and acceptable pore size. Vickers microhardness and tensile test results indicate that the optimal process parameters obtained in the current study can be suitably used in industries.
Engineering properties of rock salt and simplified closed-form deformation solution for circular opening in rock salt under the true triaxial stress state
Singh A., Kumar C., Gopi Kannan L., Seshagiri Rao K., Ayothiraman R.
Article, Engineering Geology, 2018, DOI Link
View abstract ⏷
Underground structures and storage caverns are increasingly being constructed in rock salt due to its unique self-healing ability and impervious nature. Rock salts are likely to experience and develop time-dependent behavior/deformation. Hence, the characterization of rock salt for its properties, including viscosity, are pertinent for design of these structures. In addition, the material in underground openings experiences true-triaxial stresses and hence it is vital to study the behaviour of such structures under true-triaxial loading conditions. This paper presents results of extensive laboratory testing carried out on specimens of Khewra rock salt for its physico-mechanical properties. Physical and engineering properties such as mineralogy, density, sonic wave velocity, resistivity, point load index and shear strength properties were measured. A simplified closed-form solution which deploys three-dimensional strength criterion (Mogi-Coulomb) with Maxwell viscoelastic behaviour is developed to assess the stress and deformation behaviour of circular opening in plane strain condition. The closed-form solution assumes that the material exhibits the Maxwell behavior when the stresses are lower than the yield stress and the material behavior is the combination of Maxwell and Mogi-Coulomb elastoplastic material, when the stresses are equal to the yield stress. In addition, a cylindrical wellbore problem is solved with the proposed closed-form solution and the deformation of the wellbore was estimated for the different time intervals.
Comparison of bead shape, microstructure and mechanical properties of fiber laser beam welding of 2 mm thick plates of Ti-6Al-4V alloy
Kumar C., Das M., Paul C.P., Bindra K.S.
Article, Optics and Laser Technology, 2018, DOI Link
View abstract ⏷
Fiber laser beam welding experiments are carried out on 2 mm thick plates of Ti-6Al-4V alloy at various welding conditions. A specially designed workpiece fixture with shielding gas delivery system is fabricated and effectiveness of shielding gas is confirmed by energy dispersive X-ray spectroscopy analysis. Two different types of bead cross-sections i.e. T-shaped and nearly X-shaped beads are observed at different line energies. After experiments, width and area of fusion zone and size of heat affected zone are measured and further analyzed. The microstructural studies at different locations in heat affected zone and also in fusion zone are carried out with optical microscope and their morphologies are compared at different welding conditions using field emission scanning electron microscope. The porosities are observed in both T and X-shaped weld beads at different line energies. However, their sizes are in acceptable range as per BS EN:4678 standard. The maximum microhardness is found in fusion zone due to the presence of large amount of α′ martensite. The line energy utilization factor is higher for T-shaped bead than X-shaped bead. The tensile strength of T-shaped bead is lower than X-shaped bead due to higher non-uniformity in the distribution of plastic strain. The experimental results show that T-shaped welding conditions are favorable while considering full penetration in keyhole mode, narrower weld width and lesser heat affected zone.
Estimation of creep parameters of rock salt from uniaxial compression tests
Singh A., Kumar C., Kannan L.G., Rao K.S., Ayothiraman R.
Article, International Journal of Rock Mechanics and Mining Sciences, 2018, DOI Link
View abstract ⏷
This paper discusses an approach to predict the creep behaviour of rock salt using uniaxial compression testing machine, as the conventional creep testing equipments are expensive and scarcely available. As commonly observed in brittle rock, a distinct Kaiser effect is not found during pre-peak loading path, but after unloading a distinct Kaiser effect is observed in rock salt. In the present study, Acoustic Emissions (AE) technique is used to infer the rock salt behaviour under uniaxial compression. The AE technique used in the present study to explain the rock salt behaviour is based on a combination of Maxwell and Hooke models. Using these models, elastic and viscous parameters are calculated. The proposed model is able to predict the stress-strain response of rock salt with a fair accuracy in both loading and unloading conditions. It is observed that the viscosity has negative correlation with the strain rate and hence the calculated viscous parameters are then extrapolated. The extrapolated results of viscosity for different strain rate in the range of 10− 6.5–10− 10 s- 1 are very close with reported values from the literature and for the strain rate below 10− 10 s-1, the predictions are higher than the values reported in literature. This is due the fact that below 10− 12 s-1 strain rate, the viscosity becomes independent of the strain rate and its value becomes almost constant for 3–5 mm grain size rock salt. Hence a cutoff viscosity is proposed at a value of 1018 Pa.sec.
Fabrication and characterization of weldments AISI 304 and AISI 316 Used in industrial applications
Kant R., Mittal R., Kumar C., Rana B.S., Kumar M., Kumar R.
Conference paper, Materials Today: Proceedings, 2018, DOI Link
View abstract ⏷
Gas tungsten arc welding (GTAW) and Shield metal arc welding (SMAW) are processed by using E347-16 electrode and filler wire to prepare the dissimilar weldments. The aim of study was to measure the effect of welding parameters: current, voltage, gas flow rate, nozzle to plate distance on tensile strength (TS), grain structure and hardness. The arc voltage and welding current was selected as 40,60 and 80V and 30,45 and 60amp respectively. The welding speed was selected as 4, 8, 12cm/sec. There is zero cracks, porosity, blow holes, spatter found in welding process of plate no. 2(AISI 304 &AISI 316 with ER-309L) using non consumable tungsten electrode with argon gas and also the microstructure study shows that the welding is self cooled welding structure with fine austenitic structure and very little heat affected zone found in this process. TIG welded dissimilar joint has best joint strength, uniform hardness variation as well as joint integrity.
Flexible power transfer in smart transformer interconnected microgrids
Hrishikesan V.M., Kumar C., Liserre M.
Conference paper, Proceedings: IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society, 2018, DOI Link
View abstract ⏷
Microgrids (MGs) with large penetration of photovoltaic (PV) based distributed generation (DG) sources require improved power flow control methods due to the intermittent nature of renewable energy production. In this paper, a flexible power distribution system is proposed which introduces a medium voltage (MV) dc link connection between two smart transformers (ST) with a common battery energy storage system (BESS) configuration. The MVDC connection is achieved without extra investment in converters and this facilitates a flexible way of transferring active power between MGs. The dc power transfer offers a solution with lower power loss in comparison with three phase ac system. This also improves the overall reliability of the system by ensuring the power supply to the loads during ST MV converter failure. PSCAD simulation results are discussed to show the merits of the proposed configuration.
Smart Transformer Based Loop Power Controller in Radial Power Distribution Grid
Kumar C., Gao X., Liserre M.
Conference paper, Proceedings - 2018 IEEE PES Innovative Smart Grid Technologies Conference Europe, ISGT-Europe 2018, 2018, DOI Link
View abstract ⏷
In electric distribution grid, increased penetration of renewable energy sources (RES) and electric vehicles (EV) will create several challenging issues such as voltage limits violation in the feeder, line congestion, transformer overloading, etc. These issues could be mitigated using a loop power controller (LPC), by looping the radial distribution system. The LPC is realized either using a back-To-back power converter or with a combination of tap changer and phase shifter transformers. This paper introduces smart transformer (ST), an alternative of line frequency transformer (LFT), to additionally achieve the features of conventional LPC. The ST can achieve operational features of the conventional LPC with effective control and communication functionalities. The ST controls the active and reactive power flow in the radial distribution feeders to achieve voltage regulation in the feeder, loading balancing in the feeders, prevents LFT overloading, etc. Moreover, DC links of the ST also provide an opportunity to integrate energy storage and it allows the ST in the proposed configuration to support the grid during the peak load demand. These advantages of ST in a two feeder radial grid are validated through PSCAD based simulation studies.
Sizing and SOC Management of a Smart-Transformer-Based Energy Storage System
Kumar C., Zhu R., Buticchi G., Liserre M.
Article, IEEE Transactions on Industrial Electronics, 2018, DOI Link
View abstract ⏷
A smart transformer (ST), which is a power-electronic-based transformer with control and communication functionalities, can be the optimal solution for integrating a battery energy storage system (BESS) in an electric distribution system. In fact, a comparison of energy efficiency for the conventional BESS and the ST-based BESS is carried out, which demonstrates that the ST-based BESS operation is more efficient during charging and discharging, as compared to the conventional BESS. It has been shown that by sizing the BESS appropriately for the peak load demand, the power rating of ST converters can be reduced. The ST-based BESS provides an enhanced fault ride-through capability, as compared to the conventional BESS. However, the state of charge (SOC) of the BESS shall be correctly managed to support the peak load demand when the ST converter reaches its maximum active power rating. Both simulation and experimental results clearly verify the developed SOC management.
A Flexible and Coordinated Voltage Control Strategy for Smart Transformer
Hrishikesan V.M., Das D., Kumar C.
Conference paper, Proceedings of 2018 IEEE International Conference on Power Electronics, Drives and Energy Systems, PEDES 2018, 2018, DOI Link
View abstract ⏷
Grid voltage sags are considered to be a critical problem in power distribution system with high penetration of renewable energy resources. These voltage sags propagate through conventional power transformers (CPTs) and affect the normal operation of loads, distributed generating (DG) sources and thereby decreasing the overall reliability of the system. In this paper, a flexible and coordinated control scheme for smart transformer (ST) is proposed to regulate voltage at the medium voltage (MV) grid during both symmetrical and unsymmetrical voltage sags. The proposed scheme improves the reactive power injection capability of ST MV converter by the coordinated control of ST low voltage (LV) converter and battery energy storage system (BESS). This also isolates the ST LVAC side from the grid voltage sags and therefore, the loads and sources connected through ST are unaffected by the MV side faults. Simulation and experimental results are provided to show the efficacy of method.
Smart Transformer-based Hybrid LVAC and LVDC Interconnected Microgrid
Das D., Hrishikesan V.M., Kumar C.
Conference paper, 2018 IEEE 4th Southern Power Electronics Conference, SPEC 2018, 2018, DOI Link
View abstract ⏷
Increasing integration of renewable energy sources into the electric grid makes it necessary to develop new efficient solutions for interfacing such sources in the grid. The smart transformer (ST) is a promising solution for such a changing grid scenario. This paper proposes an ST-based hybrid low voltage AC (LVAC) and low voltage DC (LVDC) interconnected microgrid system. The available LVDC link of ST is extended in the distribution grid to realize an LVDC distribution line and the grid connected converters are connected to this proposed LVDC line. The power flow in the proposed system is investigated and a detailed performance comparison between conventional and proposed system is carried out. The proposed restructuring in the distribution grid ensures reduction in ST LV converter size, distribution losses, converter losses and control complexity of the DG converters. This scheme also helps in achieving improved voltage regulation in the LVAC line. Simulation and experimental results verify the proposed scheme.
Experimental investigation and metallographic characterization of fiber laser beam welding of Ti-6Al-4V alloy using response surface method
Kumar C., Das M., Paul C.P., Singh B.
Article, Optics and Lasers in Engineering, 2017, DOI Link
View abstract ⏷
In the present study, experimental investigations of fiber-laser-beam-welding of 5 mm thick Ti-6Al-4V alloy are carried out based on statistical design of experiments. The relationship between the process parameters such as welding power, welding speed, and defocused position of the laser beam with the output responses such as width of the fusion zone, size of the heat affected zone, and fusion zone area are established in terms of regression models. Also, the most significant process parameters and their optimum ranges are identified and their percentage contributions on output responses are calculated. It is observed that welding power and speed plays the major role for full penetration welding. Also, welding power shows direct effect whereas welding speed shows the inverse effect on the output responses. The bead geometry is influenced by the defocused position of the laser beam due to the change in power density on the workpiece surface. However, overall fusion zone area is unaffected. Mechanical characterization of the welded samples such as microstructural analysis, hardness, and tensile tests are conducted. It is noticed that the hardness value of the FZ is higher than the HAZ and BM zone due to the difference in cooling rate during welding which promotes the formation of α′ martensitic phase in the FZ. Also, an average hardness value in the FZ is compared for two different defocusing positions (i.e. 1 and 2 mm). It is found that hardness value is higher for 1 mm defocused position than 2 mm due the decrement in grain size below a critical range at 2 mm defocused position. The ultimate tensile strength and % elongation of the welded samples are degraded as compared to BM which can be further improved by post heat treatment.
Rheological Behaviour of Rock Salt under Uniaxial Compression
Singh A., Kumar C., Kannan L.G., Rao K.S., Ayothiraman R.
Conference paper, Procedia Engineering, 2017, DOI Link
View abstract ⏷
Rock salt is considered as the most suitable material for underground storage of hydrocarbons as well as the disposal sites for hazardous waste in view of its unique physical and mechanical behaviour. In India, rock salt reserves are spread sub-surface over an area of more than 50,000 sq.km. covering much of north-western region of Rajasthan. So far, limited studies on the physical and mechanical properties of rock salt in this region have been carried out. This paper discusses the behaviour of rock salt under uniaxial compression (UCS) measured from the samples collected in-situ. As reported in literature that the rock salt is likely to exhibit highly viscous behaviour, and therefore there is a need for understanding rheological behaviour of rock salt through a theoretical model. In the present study, a rheological model is proposed for predicting the stress-strain behaviour of Indian rock salt under UCS condition. Predicted stress-strain curve from the proposed rheological model using MATLAB is compared with the experimentally measured stress-strain curve. Comparison of the both experimental and predicted results indicates that proposed rheological model is able to predict stress-strain behaviour of rock salt under UCS condition. The results show that rock salt exhibits distinct time-dependent viscous behaviour and deformations.
Investigation of load compensation features of smart transformer in medium voltage grid
Kumar C., Zhu R., Liserre M.
Conference paper, Proceedings IECON 2017 - 43rd Annual Conference of the IEEE Industrial Electronics Society, 2017, DOI Link
View abstract ⏷
Harmonics and load unbalance create several adverse issues in power distribution system, which are generally mitigated by bulky shunt active power filter (SAPF). This paper explores load compensation features of smart transformer (ST) in a two-feeder city center, where conventional power transformer (CPT) in one feeder is replaced by the ST whereas other feeder is continued to be supplied through the CPT. The ST is controlled not only to supply its own loads connected at the low voltage side, but also to compensate reactive, unbalance and nonlinear loads of the other feeder. This makes total MV grid currents of the combined city center balanced, sinusoidal, and in unity power factor at the point of common coupling (PCC) voltage. Therefore, in addition to providing continuous and reliable support to the ST based loads, the ST eliminates need of bulky SAPF and isolation transformer from the city center which are used for achieving reactive and harmonic current compensation. A switching model of the system is developed in power system computer aided design (PSCAD) software and implemented on a developed experimental prototype to show the capability of the ST.
Operation and control of smart transformer-based electric vehicles charging system
Kumar C., Buticchi G., Liserre M.
Conference paper, Proceedings IECON 2017 - 43rd Annual Conference of the IEEE Industrial Electronics Society, 2017, DOI Link
View abstract ⏷
Integration of charging stations for electric vehicles (EVs) will result in severe stress on electric grid. The EVs connected to the grid can also act as a source of energy and this demands greater control as well as coordination for better utilization. Conventional power transformers (CPTs) utilized in the EV charging stations are not well equipped for meeting these challenges. Recently, smart transformer (ST) has been proposed as an alternative to CPT. The ST connects medium voltage (MV) grid to low voltage (LV) grid with two intermediate MV and LV dc links. This paper utilizes the availability of the dc links of the ST to integrate the EVs charging station to electric grid rather than connecting these through the CPTs to the grid. A comprehensive analysis of sizing of the power converters utilized in the considered system has been presented. A comparison of efficiency for the different configurations is carried out and the possible more efficient scenario is suggested. Infact, the ST based EV charging system is found to be more efficient in comparison to CPT based EV charging station. The performance of ST based EV charging station is verified through simulation studies.
Voltage quality improvement in smart transformer integrated distribution grid
Hrishikesan V.M., Kumar C., Liserre M.
Conference paper, Proceedings IECON 2017 - 43rd Annual Conference of the IEEE Industrial Electronics Society, 2017, DOI Link
View abstract ⏷
With increased penetration of renewable energy sources in electric grid, maintaining quality voltage at the load terminal has become a challenge. Voltage disturbances like sag, swell, harmonics, etc., can propagate from one section to another section of electric grid and degrade the performance of sensitive loads. This paper explores the capability of smart transformer (ST) to improve the voltage quality in medium voltage (MV) grid, by replacing one conventional power transformer (CPT) with an ST in a multifeeder electric grid. In addition to supplying ST low voltage loads, the voltage regulation in MV grid is achieved by controlling the reactive current injection to the MV grid. Harmonic damping capability is integrated with the control loop to damp out the grid voltage harmonics. An improved stability of MV grid voltage regulation control is achieved in the presence of harmonic damping loop and this is verified with theoretical analysis. Extensive simulation study is carried out to validate the ST features.
Power management in a ST integrated medium voltage grid
Hrishikesan V.M., Kumar C.
Conference paper, 2017 National Power Electronics Conference, NPEC 2017, 2017, DOI Link
View abstract ⏷
High penetration of distributed generation (DG) sources result in bidirectional power flow and conventional power transformer (CPT) based microgrid experiences lack of controllability features in terms of real and reactive power flow between multiple feeders. This, in turn leads to voltage rise or fall depending upon different DG operating scenarios. This paper focus on the performance improvement in a smart transformer (ST) based medium voltage (MV) microgrid with DG connected multiple feeders. The ST capability for integrating battery energy storage system (BESS) is utilized to control the power flow in a multi-feeder distribution system.
Operation and control of smart transformer based distribution grid in a microgrid system
Conference paper, 2017 National Power Electronics Conference, NPEC 2017, 2017, DOI Link
View abstract ⏷
The smart transformer (ST) has been studied extensively in recent years exploring its capabilities in the modern electric grid. Concentrating on the low voltage (LV) side of an ST, this paper proposes a grid structure where a photovoltaic (PV) system and battery energy storage system (BESS) are interfaced to the ST LV DC link. The LV AC grid consists of AC loads and a microgrid with a PV unit and DC loads. Investigation is done on how an ST can achieve proper power management, in addition to carrying out the functions of a conventional transformer on the LV side. A PSCAD simulation of the proposed grid structure is carried out and the operation of the system in the various power flow scenarios is verified. The paper also emphasizes the capability of ST to eliminate the need of other power quality improvement devices in the distribution grid by maintaining the appropriate voltages in the LV grid.
LCL filter based UPQC configuration for power quality improvement
Kumar C., Mishra M.K., Liserre M.
Conference paper, IEEE Power and Energy Society General Meeting, 2016, DOI Link
View abstract ⏷
This paper proposes a unified power quality conditioner (UPQC) configuration employing an LCL filter at front of shunt voltage source inverter (VSI). As compared to conventional UPQC with L filter at the front of the shunt VSI, the proposed UPQC provides improved compensation while using much smaller value of filter inductance. With the smaller filter inductance, voltage requirement of common dc link also gets reduced. It results in reduced switching losses in the series and shunt VSIs. Therefore, proposed UPQC achieves reduction in weight, cost, size, and losses while providing improved current compensation capability. Simulation results are presented to verify all the features.
Detecting Low Frequency Oscillations through PMU-based measurements for Indian National Grid
Mukhopadhyay S., Agrawal V.K., Soonee S.K., Agarwal P.K., Anumasula R., Kumar C.
Conference paper, 19th Power Systems Computation Conference, PSCC 2016, 2016, DOI Link
View abstract ⏷
Indian National Grid formed with the connection of Southern Grid to the rest of India in the last phase on December 31, 2013 ushered in having improved frequency regime of operation as well as large inter-regional power transfer for optimal operation. But problems of Low Frequency Oscillations continued to be observed in several parts. Wide-Area Monitoring System with large-scale deployment of Phasor Measurement Units, made it possible to detect such oscillations at specific locations and evolve remedial measures to be undertaken. Under long-term strategy investment-oriented strengthening of transmission system is the choice. But to deal with such problems for day-to-day operation, tuning or retuning of Power System Stabilizers, controllers associated with Flexible AC Transmission Systems and HVDC Systems, etc. are considered as the best option. Commensurate Regulatory Framework too is expected to be made for handling such issues from the point of view of Plant-Grid Interaction.
Design of External Inductor for Improving Performance of Voltage-Controlled DSTATCOM
Kumar C., Mishra M.K., Liserre M.
Article, IEEE Transactions on Industrial Electronics, 2016, DOI Link
View abstract ⏷
A distribution static compensator (DSTATCOM) is used for load voltage regulation, and its performance mainly depends upon the feeder impedance and its nature (resistive, inductive, stiff, nonstiff). However, a study for analyzing voltage regulation performance of DSTATCOM depending upon network parameters is not well defined. This paper aims to provide a comprehensive study of design, operation, and flexible control of a DSTATCOM operating in voltage control mode. A detailed analysis of the voltage regulation capability of DSTATCOM under various feeder impedances is presented. Then, a benchmark design procedure to compute the value of external inductor is presented. A dynamic reference load voltage generation scheme is also developed, which allows DSTATCOM to compensate load reactive power during normal operation, in addition to providing voltage support during disturbances. Simulation and experimental results validate the effectiveness of the proposed scheme.
Smart transformer-based hybrid grid loads support in partial disconnection of MV/HV power system
Kumar C., Zou Z., Liserre M.
Conference paper, ECCE 2016 - IEEE Energy Conversion Congress and Exposition, Proceedings, 2016, DOI Link
View abstract ⏷
Double circuit lines are common for transmitting the electrical power in high voltage (HV) and/or medium voltage (MV) power system. During the faults in one of the lines or transformers of the double circuit lines, one line is disconnected from the system and the healthy line is utilized for supplying the entire load. In that case, the transformer supplying the entire load could be overloaded. For the safe operation of the transformer, it is needed to disconnect some of the loads. This partial disconnection of MV/HV power system can severally effect the performance of critical loads. Recently, power electronic based transformer equipped with effective control and communication called smart transformer (ST) has been proposed for installation in the distribution system in place of conventional transformer. One of the most important feature of ST is to allow for connection of ac and dc grid forming hybrid grid which allow easy integration of renewable energy sources and storage. Considering these feature of ST, this paper proposes a new functionality of the ST where it provides continuous power to a section of the loads during the partial disconnection of MV/HV power system and improves the performance of power system. This new feature of ST has been proved through power system computer aided design (PSCAD) software based simulation results. Power hardware in loop (PHIL) and control hardware in loop (CHIL) is under development to test the idea.
A 3-D Finite Element Analysis of Transient Temperature Profile of Laser Welded Ti-6Al-4V Alloy
Kumar C., Das M., Biswas P.
Book chapter, Topics in Mining, Metallurgy and Materials Engineering, 2015, DOI Link
View abstract ⏷
In this work, a numerical investigation of transient temperature profile of Laser beam welding process is carried out. A 3-D finite element modelling is developed considering combined double-ellipsoidal heat source model for both spot and moving heat sources. The temperature dependent thermo-physical material properties of Ti-6Al-4V alloy are incorporated. The effect of latent heat of fusion and convective and radiative boundary conditions are considered. The effect of laser beam power on the transient temperature profile and the dimensions of the heat affected zone are analysed. From finite element simulation, it is observed that the peak temperature in the fusion zone increases with increased laser beam power. Also, the size of the heat affected zone strongly depends on the power of the laser beam.
Operation and Control of an Improved Performance Interactive DSTATCOM
Article, IEEE Transactions on Industrial Electronics, 2015, DOI Link
View abstract ⏷
This paper proposes an improved performance interactive distribution static compensator (DSTATCOM) to address the limitations of conventional current control mode (CCM) and voltage control mode (VCM) operations. The proposed interactive scheme provides smooth transfer of modes of operation while remaining connected in the distribution system. In normal operation, the DSTATCOM operates in CCM to make source currents balanced, sinusoidal, and at a unity power factor. During voltage disturbances, the CCM operation cannot improve load voltage. In that case, DSTATCOM operation is changed to VCM, which maintains a constant voltage across the sensitive loads. Hence, this interactive DSTATCOM ensures continuous, flexible, and robust operation of the load. Moreover, the filter current requirements are reduced in the proposed scheme, which reduces the losses in the filter and feeder, improves inverter efficiency, and requires a reduced-rating inverter for sag mitigation. The principle of operation and control for both operating modes is analyzed. The detailed process of the flexible transfer between the two modes is derived. Deadbeat predictive control algorithms for CCM as well as VCM operation are developed for fast operation during mode transfers. The performance of the proposed scheme is validated by both simulation and experimental results.
Operation and control of smart transformer for improving performance of medium voltage power distribution system
Conference paper, 2015 IEEE 6th International Symposium on Power Electronics for Distributed Generation Systems, PEDG 2015, 2015, DOI Link
View abstract ⏷
Smart transformer (ST) is a power electronic based transformer equipped with effective control and communication. It is expected to play a significant role in future power distribution system, however, their operational features in the medium voltage (MV) power distribution systems are yet not explored. In this paper, operation and control of ST are presented for improving its performance and operational range in a power distribution system consisting of two radial feeders in a city center. For investigating the performance of ST in above system, one conventional power transformer (CPT) is replaced by the ST whereas other feeder is continued to be supplied through the CPT. In this scheme, the ST is operated such that it makes total MV grid currents of the combined system balanced sinusoidal with unity power factor. Therefore, in addition to providing continuous and reliable operation of ST based loads, the ST can also improve the performance of the loads which are supplied by the CPT in a different feeder. Moreover, the proposed scheme eliminates the need of power quality improvement devices at the other feeder. Therefore, the scheme also makes the application of ST in the distribution system cost effective. Simulation results validate the suitability of ST in improving the performance of multiple feeder medium voltage power distribution system.
A dual three-leg VSI based DSTATCOM in three-phase four-wire distribution systems
Kumar M.V.M., Mishra M.K., Kumar C.
Conference paper, 2015 IEEE 6th International Symposium on Power Electronics for Distributed Generation Systems, PEDG 2015, 2015, DOI Link
View abstract ⏷
This paper proposes a dual three-leg voltage source inverter (VSI) based distribution static compensator (DSTAT-COM) to compensate unbalanced and nonlinear loads in three-phase four-wire distribution systems. The proposed topology uses two three-leg inverters having common dc-link with single dc capacitor and an additional small capacitor connected from the negative terminal of VSI to the system neutral. The proposed scheme with associated control algorithm has the capability to compensate unbalanced nonlinear load and hence makes source current as balanced sinusoidal and at desired power factor. The control algorithm also ensures the proper sharing of reactive, harmonics and unbalance powers between two VSIs and controls the grid current total harmonic distortion (THD) level. The performance of the proposed scheme has been verified using simulation and experimental studies and results are presented.
A control scheme to enhance DSTATCOM operation in power distribution system
Kumar C., Kumar M.V.M., Mishra M.K.
Conference paper, 2015 IEEE 6th International Symposium on Power Electronics for Distributed Generation Systems, PEDG 2015, 2015, DOI Link
View abstract ⏷
This paper proposes a hybrid control algorithm to maximize utilization and functionality of distribution static compensator (DSTATCOM). This control algorithm combines the different aspects of DSTATCOM operation and tries to mitigate the voltage and current harmonics, balance the source currents, improve the power factor, compensate for voltage disturbances such as sag and swell, reduce the losses and rating of inverter, and control the load power for energy conservation while analyzing their effects on the consumers. Moreover, at any time of operation, performance of proposed control algorithm based DSTATCOM is superior compared to its conventional counterparts. With all these advantages, proposed scheme provide a promising solution to enhance the operation of power distribution system. Detailed simulation results are presented to validate the performance of the proposed scheme.
Enhanced utilization of grid-connected inverter
Kumar C., Mishra M.K., Kumar M.V.M.
Conference paper, 2015 IEEE 6th International Symposium on Power Electronics for Distributed Generation Systems, PEDG 2015, 2015, DOI Link
View abstract ⏷
Smooth mode transfer of voltage source inverter (VSI) between grid-connected and stand-alone modes is achieved by operating the inverter in voltage control mode (VCM). However, this operation produces some adverse practical issues such as requirement of large rating VSI, limited real power injection by VSI, negligible operational capability in strong grid, frequent mode transfer, and reactive power exchange with the grid even at nominal grid voltage. This paper proposes a grid-connected inverter to address these issues. An external inductor, satisfying several constraints, is proposed between the load and grid points to enhance the capability of inverter to operate in VCM during voltage disturbances as well as in adverse grid conditions. Also, an improved control algorithm is proposed for reference load voltage generation. This algorithm enables inverter to provide advantages of current control mode (CCM) during normal operation such that grid exchanges only real power; and VCM during grid disturbances by maintaining constant voltage at the load terminal. Moreover, inverter continues to inject DG power for the entire operation. Grid-connected inverter becomes multifunctional with these features resulting in enhanced utilization. This is validated by simulation results.
Predictive Voltage Control of Transformerless Dynamic Voltage Restorer
Article, IEEE Transactions on Industrial Electronics, 2015, DOI Link
View abstract ⏷
This paper presents a predictive voltage control scheme for the effective control of a transformerless dynamic voltage restorer (TDVR). This control scheme utilizes the discrete model of a voltage source inverter and an interfacing filter for the generation of the switching strategy of inverter switches. Predictive voltage control algorithm-based TDVR tracks the reference voltage effectively and maintains load voltages sinusoidal during various voltage disturbances as well as load conditions. Moreover, this scheme does not require any linear controller or modulation technique. Simulation and experimental results are presented to verify the performance of the proposed scheme.
A Grid-Connected Dual Voltage Source Inverter with Power Quality Improvement Features
Manoj Kumar M.V., Mishra M.K., Kumar C.
Article, IEEE Transactions on Sustainable Energy, 2015, DOI Link
View abstract ⏷
This paper presents a dual voltage source inverter (DVSI) scheme to enhance the power quality and reliability of the microgrid system. The proposed scheme is comprised of two inverters, which enables the microgrid to exchange power generated by the distributed energy resources (DERs) and also to compensate the local unbalanced and nonlinear load. The control algorithms are developed based on instantaneous symmetrical component theory (ISCT) to operate DVSI in grid sharing and grid injecting modes. The proposed scheme has increased reliability, lower bandwidth requirement of the main inverter, lower cost due to reduction in filter size, and better utilization of microgrid power while using reduced dc-link voltage rating for the main inverter. These features make the DVSI scheme a promising option for microgrid supplying sensitive loads. The topology and control algorithm are validated through extensive simulation and experimental results.
A new prospective of smart transformer application: Dual microgrid (DMG) operation
Conference paper, IECON 2015 - 41st Annual Conference of the IEEE Industrial Electronics Society, 2015, DOI Link
View abstract ⏷
With the significant increase in renewable energy sources (RES) and storage elements, power distribution system needs new services for reliable and continuous operation. Smart transformer (ST) based on power electronics, control, and communication has been proposed for improving the performance of power system. However, operational capabilities and applications of ST with RES and energy storage in distribution system are still not explored in detail. In this paper, a new prospective of ST application, dual microgrid (DMG) operation, is proposed. In normal medium voltage (MV) grid operation, the ST supplies power to loads connected to its low voltage side and injects into the MV grid depending upon the available RES and load demand. During the voltage disturbances, the ST feeds power to the sensitive loads connected to the other feeders equipped with the conventional power transformers. In this case, the distribution loads are isolated from the MV utility grid. This ability of the smart transformer to isolate from the utility grid and provide continuous power to the sensitive loads of other feeders has potential to significantly improve the performance of power system as well as ST. With simulation results based on PSCAD/EMTDC software, this paper introduces for the first time an unexplored feature of the smart transformer.
An improved hybrid DSTATCOM topology to compensate reactive and nonlinear loads
Article, IEEE Transactions on Industrial Electronics, 2014, DOI Link
View abstract ⏷
This paper proposes an improved hybrid distribution static compensator (DSTATCOM) topology to address some practical issues such as power rating, filter size, compensation performance, and power loss. An LCL filter has been used at the front end of a voltage source inverter (VSI), which provides better switching harmonics elimination while using much smaller value of an inductor as compared with the traditional L filter. A capacitor is used in series with an LCL filter to reduce the dc-link voltage of the DSTATCOM. This consequently reduces the power rating of the VSI. With reduced dc-link voltage, the voltage across the shunt capacitor of the LCL filter will be also less. It will reduce the power losses in the damping resistor as compared with the traditional LCL filter with passive damping. Therefore, the proposed DSTATCOM topology will have reduced weight, cost, rating, and size with improved efficiency and current compensation capability compared with the traditional topology. A systematic procedure to design the components of the passive filter has been presented. The effectiveness of the proposed DSTATCOM topology over traditional topologies is validated through both simulation and experimental studies.
Dual-functional DSTATCOM with flexible mode transfer for power quality improvement
Conference paper, IEEE Power and Energy Society General Meeting, 2014, DOI Link
View abstract ⏷
This paper proposes a dual-functional distribution static compensator (DSTATCOM) with flexible mode transfer between current control mode (CCM) and voltage control mode (VCM). The DSTATCOM operates in CCM within a range of load voltage to provide load balancing, power factor correction, and load harmonic elimination. In the VCM, the DSTATCOM regulates load voltage at a reference value to protect sensitive loads from voltage disturbances. A control algorithm has been proposed to obtain the appropriate range of source voltage for which DSTATCOM operates in CCM. Outside this voltage range, DSTATCOM operates in VCM. The proposed algorithm with the dual-functional DSTATCOM exhibit various operational characteristics such that 1) source currents are balanced, sinusoidal, and in phase with respective phase load voltages for a defined range of source voltage; 2) load harmonic and reactive current components are always supplied by the compensator; and 3) load voltage is maintained at a constant voltage during voltage disturbance for protection of sensitive loads. Simulation results are provided to demonstrate the performance of the proposed algorithm and dual-functional DSTATCOM.
A simple digital control algorithm for three phase shunt active filter: Simulation and experimentation
Srinath S., Kumar C., Selvan M.P.
Article, Frontiers in Energy, 2014, DOI Link
View abstract ⏷
A novel and simple i freal control algorithm using digital signal processor (DSP) has been proposed and realized for a three phase shunt active filter (SAF). The simulation and prototype construction of SAF is conducted to compensate the reactive power and harmonics in a distribution system. The major feature of the proposed i freal algorithm is that it does not require unit vector templates and any transformations for the reference current generation of SAF. This reduces the computational complexity and makes the control flexible and faster. The simulation is conducted in MATLAB/SIMULINK while DSP TMS320LF2407 is employed in the digital implementation of hysteresis current control (HCC) for experimentation. The hardware results correlate with the simulation results in reducing the total harmonic distortion (THD) of the source current and achieving unity power factor. © 2013 Higher Education Press and Springer-Verlag Berlin Heidelberg.
A multifunctional DSTATCOM operating under stiff source
Article, IEEE Transactions on Industrial Electronics, 2014, DOI Link
View abstract ⏷
Loads connected to a stiff source cannot be protected from voltage disturbances using a distribution static compensator (DSTATCOM). In this paper, a new control-algorithm-based multifunctional DSTATCOM is proposed to operate in voltage control mode under stiff source. This scheme provides fast voltage regulation at the load terminal during voltage disturbances and protects critical loads. In addition, during normal operation, the generated reference load voltages allow control of the source currents. Consequently, DSTATCOM injects reactive and harmonic components of load currents to make source power factor unity. Simulation and experimental results are presented to verify the efficacy of the proposed control algorithm and multifunctional DSTATCOM. © 2013 IEEE.
A voltage-controlled DSTATCOM for power-quality improvement
Article, IEEE Transactions on Power Delivery, 2014, DOI Link
View abstract ⏷
This paper proposes a new algorithm to generate reference voltage for a distribution static compensator (DSTATCOM) operating in voltage-control mode. The proposed scheme exhibits several advantages compared to traditional voltage-controlled DSTATCOM where the reference voltage is arbitrarily taken as 1.0 p.u. The proposed scheme ensures that unity power factor (UPF) is achieved at the load terminal during nominal operation, which is not possible in the traditional method. Also, the compensator injects lower currents and, therefore, reduces losses in the feeder and voltage-source inverter. Further, a saving in the rating of DSTATCOM is achieved which increases its capacity to mitigate voltage sag. Nearly UPF is maintained, while regulating voltage at the load terminal, during load change. The state-space model of DSTATCOM is incorporated with the deadbeat predictive controller for fast load voltage regulation during voltage disturbances. With these features, this scheme allows DSTATCOM to tackle power-quality issues by providing power factor correction, harmonic elimination, load balancing, and voltage regulation based on the load requirement. Simulation and experimental results are presented to demonstrate the efficacy of the proposed algorithm. © 1986-2012 IEEE.
Reply to the discussion on “Evaluation of selected equations for predicting scour at downstream of ski-jump spillway using laboratory and field data” [Engineering Geology 129-130 (2012) 98-103]
Note, Engineering Geology, 2013, DOI Link
Reply to the Comments on “Evaluation of selected equations for predicting scour at downstream of ski-jump spillway using laboratory and field data” by Chandan Kumar, P. Sreeja [Engineering Geology 129-130 (2012) 98-103]
Note, Engineering Geology, 2013, DOI Link
A multi-functional DSTATCOM operating in voltage control mode
Conference paper, 2013 IEEE 8th International Conference on Industrial and Information Systems, ICIIS 2013 - Conference Proceedings, 2013, DOI Link
View abstract ⏷
This paper investigates the challenges in mitigating several power quality (PQ) problems by a single distribution static compensator (DSTATCOM), and proposes a reduced rating voltage controlled hybrid DSTATCOM with multi-functional features. This scheme connects a suitably designed external inductor, as a part of the load, between the source and load points. This inductor improves the voltage regulation bandwidth of DSTATCOM and reduces the current requirement for voltage sag mitigation. Along with this, a multi-functional algorithm is proposed to generate dynamic reference load voltage. This algorithm indirectly controls the source currents during normal operation to mitigate current related PQ problems, whereas maintains a constant voltage at the load terminal during voltage disturbances. Simulation results are presented to validate the capability of single DSTATCOM to mitigate several PQ problems. © 2013 IEEE.
Energy conservation and power quality improvement with voltage controlled DSTATCOM
Conference paper, 2013 Annual IEEE India Conference, INDICON 2013, 2013, DOI Link
View abstract ⏷
This paper proposes a new scheme to generate reference voltage for a existing DSTATCOM operating in voltage control mode (VCM). The proposed method provides DSTAT-COM an energy conservation (EC) feature while enhancing its power quality (PQ) improvement capability without using any extra circuitry. With this scheme, power drawn by the load decreases which reduces the tariff, reduces heating losses in load, and increases their life. Also, it will reduce the utility power requirement, greenhouse gas production, and increases energy efficiency, all of them are utility benefits. As DSTATCOM is installed by end users, incentives can be obtained from the utility with this scheme. This scheme ensures that during nominal operation unity power factor (UPF) is achieved at load terminal, which is not possible in traditional method. Also, compensator injects lesser currents, therefore, reduces losses in feeder and inverter. Further, a saving in rating of DSTATCOM is achieved which increases its capacity to mitigate deep voltage sag. Simulation results are presented to demonstrate the efficacy of the proposed scheme. © 2013 IEEE.
A modified DSTATCOM topology with reduced VSI rating, DC link voltage, and filter size
Conference paper, 4th International Conference on Clean Electrical Power: Renewable Energy Resources Impact, ICCEP 2013, 2013, DOI Link
View abstract ⏷
Rating of voltage source inverter (VSI) and size of the interfacing filter are two important issues while implementing DSTATCOM. In this paper, a new DSTATCOM topology has been proposed which simultaneously reduces the rating of VSI as well as size of interfacing filter with enhanced current compensation capabilities. A capacitor is used in series with interfacing filter to reduce the dc link voltage of the DSTATCOM. Therefore, rating of VSI gets reduced as it is directly proportional to dc link voltage. To reduce the size of interfacing filter, an LCL filter has been used. An LCL filter provides excellent switching harmonics elimination capability while using much smaller value of inductor as compared to conventional L filter. A smaller inductance will cause small voltage drop across it which in turn further reduces the size of dc bus voltage and consequently VSI rating. Therefore, proposed topology will reduce weight, cost, rating, and size of the DSTATCOM with enhanced current compensation capability compared to conventional topology. A procedure to design LCL filter parameters and series capacitor has been presented. Effectiveness of the proposed DSTATCOM topology over traditional topology is verified through extensive simulation using PSCAD/EMTDC. © 2013 IEEE.
Evaluation of selected equations for predicting scour at downstream of ski-jump spillway using laboratory and field data
Article, Engineering Geology, 2012, DOI Link
View abstract ⏷
The provision of spillways in the structure of a dam enables proper disposal of flood water in excess of the reservoir capacity, and regulates the energy of flowing water downstream. Some spillways dissipate energy in the form of ski-jump which leads to scouring process. Scour holes formed downstream of spillways may affect the safety and stability of the structure. Therefore accurate prediction of the scour depth is necessary to ensure the safety of dam as well as its abutments. The prediction procedure is extremely complex due to various hydraulic and geological factors influencing scouring phenomenon. Several researchers have developed empirical equations for scour depth predictions, keeping in view the above mentioned factors. It is noted from the literature that there are not many studies to evaluate the efficiency of these equations for scour depth prediction. Therefore, the present study attempts to evaluate different empirical equations available in the literature for scour depth prediction using experimental and field data reported in the literature. For this purpose, a database has been formulated based on the scour depth values reported in the literature. © 2012 Elsevier B.V..
A control algorithm for flexible operation of DSTATCOM for power quality improvement in voltage and current control mode
Conference paper, PEDES 2012 - IEEE International Conference on Power Electronics, Drives and Energy Systems, 2012, DOI Link
View abstract ⏷
Distribution Static Compensator (DSTATCOM) is used for power factor correction, voltage regulation, load balancing, and harmonic elimination. A DSTATCOM can not fulfill all these objectives simultaneously. In the presented work, authors have proposed a control algorithm for dual functional DSTATCOM that enables it to operate either in current control mode (CCM) or in voltage control mode (VCM). A new control algorithm has been devised that allows DSTATCOM to smoothly switch over from CCM to VCM and vice versa. In VCM it regulates load terminal voltage at a desired magnitude, whereas in CCM it injects reactive and harmonics current such that supply sees unity power factor. PSCAD/EMTDC software is used for extensive simulation studies and results of DSTATCOM operation in VCM, CCM, and transition from one mode to another mode are presented in detail. © 2012 IEEE.
Digital feedback control based dynamic voltage compensator for voltage sag mitigation: Simulation and experimental validation
Srinath S., Kumar C., Selvan M.P.
Conference paper, 2012 IEEE 7th International Conference on Industrial and Information Systems, ICIIS 2012, 2012, DOI Link
View abstract ⏷
This paper deals with the voltage sag mitigation for a fixed sensitive load by using a Dynamic Voltage Compensator (DVC) connected to the distribution system. DVC consists a power electronic controller, protecting critical loads from disturbances occurring in the supply system and regulating the load voltage against any sag in the supply. The proposed work is confined to balanced sinusoidal systems and unique in not using any transformations to generate the reference voltage. The steady state analysis is considered and the simulation results are presented in MATLAB / SIMULINK. A simple digital feedback control algorithm is formulated using the digital signal processor (DSP) TMS320LF2407. The reference voltage is determined based on the output voltage of suitably designed LEM voltage sensors, leading to simple hardware with reduced computation. The reference signals are tracked using a fixed hysteresis band control and the DVC is realized using three single phase voltage source inverters (VSI). © 2012 IEEE.
Dynamic Voltage Compensator: Transformationless control perspective
Srinath S., Kumar C., Selvan M.P.
Conference paper, 2011 IEEE PES International Conference on Innovative Smart Grid Technologies-India, ISGT India 2011, 2011, DOI Link
View abstract ⏷
The impact of voltage quality on the operation of sensitive equipment is very critical. Dynamic Voltage Compensator (DVC) is the prime solution to mitigate the voltage quality problems. This paper investigates the compensation performance of a DVC connected to a distribution system, equipped with a simple control based on in-phase compensation and without using any transformations for reference generation. The efficacy of the controller under steady state operation to mitigate voltage sag, swell and unbalance is analyzed through intensive simulation in MATLAB/SIMULINK. The present investigation is confined to balanced sinusoidal systems with a fixed balanced load. The transformation less approach leads to simple control with reduced computation. © 2011 IEEE.
Effects of ethanol addition on performance, emission and combustion of di diesel engine running at different injection pressures
Kumar C., Athawe M., Aghav Y.V., Gajendra Babu M.K., Das L.M.
Conference paper, SAE Technical Papers, 2007, DOI Link
View abstract ⏷
Ethanol is an alternative renewable fuel produced from various agricultural products. Ethanol-diesel emulsion technique is used for the utilization of ethanol in diesel engines wherein ethanol is used without any modification. The performance, combustion and emission characteristics of a direct injection (DI) diesel engine for off-highway application were evaluated using ethanol-diesel microemulsions. The addition of ethanol to diesel fuel simultaneously decreases calorific value, kinematic viscosity and stability of fuel. Ethyl acetate was used as an additive/ingredient to keep the blends in homogeneous and stable state. Blends (D80/E13/EA07; D70/E17/EA13; D60/E23/EA17) were selected for engine experiments based on stability behavior and fuel properties. The results showed no significant power reduction in the engine operation with ethanol-diesel microemulsions. Although, brake specific fuel consumption (BSFC) increased, improvement was observed in the brake specific energy consumption (BSEC). The thermal efficiency also improved significantly at lower loads. NOx and smoke emissions were reduced by 5-10% and 15-50%, respectively. UBHC and CO deteriorated especially at lower loads but improved at higher loads. From the combustion analysis, it was observed that the use of ethanol blended diesel fuel prolonged the ignition delay along with shortening of total combustion duration. Studies conducted at different injection pressures (200, 250, 300 and 350 bar) on different loading conditions showed that the higher injection pressure reduces CO and smoke emissions with respect to diesel fuel. Copyright © 2007 SAE International.
Experimental investigations on a karanja oil methyl ester fueled DI diesel engine
Kumar C., Gajendra Babu M.K., Das L.M.
Conference paper, SAE Technical Papers, 2006, DOI Link
View abstract ⏷
The methyl ester of karanja oil, known as biodiesel, is receiving increasing attention as an alternative fuel for diesel engine. This paper presents the results of investigations carried out in studying the fuel properties of karanja oil methyl ester (KOME) and its blend with diesel from 20% to 80% by volume and in running a DI diesel engine with these fuels. Engine tests have been carried out with the aim of obtaining performance characteristics such as Brake specific fuel consumption(BSFC), brake thermal efficiency, brake power, exhaust gas temperature, emission such as CO, UBHC, NOx, smoke opacity and combustion parameters to evaluate and compute the behavior of the diesel engine running on KOME and its blends with diesel fuel. The addition of KOME to diesel fuel has significantly reduced CO, UBHC and smoke emissions but it increases the NOx emission slightly. The results show that: no significant power reduction in the engine operation when operated with blends of KOME and diesel fuel. Although there is a slight increase in brake specific fuel consumption (BSFC), brake specific energy consumption (BSEC) has improved. The brake thermal efficiency also improved remarkably at B20 and B40. Copyright © 2006 SAE International.
Exhaust emission characteristics of a constant speed SI engine on denatured anhydrous and aqueous ethanol of different proofs
Bhattacharya T.K., Kumar C., Mishra T.N.
Article, Journal of the Institution of Engineers (India): Chemical Engineering Division, 2005,
View abstract ⏷
Denatured anhydrous and aqueous ethanol of 200°, 190°, 180°and 170° proof has been burnt in a constant speed SI engine designed to operate on kerosene. The effect of water content in the fuel on engine exhaust emissions has been studied. The emission of carbon monoxide is found to be 14.0%-23.7% lower and a decrease in unburnt hydrocarbon emission from 99% to 29% is observed on denatured ethanol of different proofs as compared to that observed on kerosene. The emission of NOx is found to be higher on denatured ethanol of different proofs. However, it is comparable with kerosene when engine is operated on 170° proof ethanol.
